Myson 325 Tankless manual

Part No. 27/19243 - 03

Installation, Service & Users InstructionsInstallation, Service & Users InstructionsInstallation, Service & Users InstructionsInstallation, Service & Users InstructionsInstallation, Service & Users Instructions

Myson 325 NG/LPEnergy Saving Tankless Gas Water Heaters

WARNING: If the information in these instructions are not followed exactly, a fire orexplosion may result causing property damage, personal injury or death.

- Do not store or use gasoline or other flammable vapors and liquids in the vicinityof this or any other appliance.

- WHAT TO DO IF YOU SMELL GAS

Do not try to light any appliance. Do not touch any electrical switch; do not use any phone in your building. Immediately call your gas supplier from a neighbor's phone. Follow the gas

supplier's instructions. If you cannot reach your gas supplier, call the fire department.

- Installation and service must be performed by a qualified installer, service agencyor the gas supplier.

'NRTL'

The polythene bags used for packaging are a potential hazard to babies and young childrenand MUST BE DISPOSED OF IMMEDIATELY.

WARNINGDo not use this appliance if any part has been under water. Immediately call a qualifiedservice technician to inspect the appliance and to replace any part of the control system andany gas control which has been under water.

INSTALLERINSTALLERINSTALLERINSTALLERINSTALLERAffix these instructions to orAffix these instructions to orAffix these instructions to orAffix these instructions to orAffix these instructions to or

adjacent to the appliance.adjacent to the appliance.adjacent to the appliance.adjacent to the appliance.adjacent to the appliance.

OWNEROWNEROWNEROWNEROWNERRetain these instructions safelyRetain these instructions safelyRetain these instructions safelyRetain these instructions safelyRetain these instructions safely

for future reference.for future reference.for future reference.for future reference.for future reference.

McNeelMcNeelMcNeelMcNeelMcNeely-Yy-Yy-Yy-Yy-Yuill Corporationuill Corporationuill Corporationuill Corporationuill CorporationMyson "Tankless" Gas Hot Water Heaters9911 Horn Road, Suite "100"Sacramento, Ca., 95827

For More Information Telephone: 916/362 - 1671TeleFax: 916/362 - 1698

CF 325 Nat Gas (55-61) - CF 325-LP L.P. Gas (55-62)DV 325 Nat Gas (55-63) - DV 325-LP L.P. Gas (55-64)

2 Part No. 27/19243Important Requirements - All Models

Important Requirements - All Models

- The Myson 325 water heater must be kept from freezing. It must be installed in an area freefrom freezing or a heated room. Freezing can severely damage the heater and will void thewarranty.

- The appliance should be located in an area where leakage of the water piping will not resultin damage to the area adjacent to the water heater or to lower floors of the structure. Whensuch locations cannot be avoided, it is recommended that a suitable drain pan, adequatelydrained, be installed under the water heater. The pan must not restrict combustion airflow.

- The appliance shall be isolated from the gas supply piping system during any pressuretesting of that system.

- The appliance and its gas connection shall be leak tested before placing the appliance inoperation.

- DO NOT obstruct the flow of combustion or ventilating air to the heater.

High Altitude Installation: For installations between 2,000 - 4,500 ft (610 - 1,370m)CONSULT the McNeely-Yuill Corporation, telephone 916-362-1671.

IMPORTANT: This appliance must be installed by a person suitably qualified in the installationof gas appliances. This appliance must be installed in accordance with local codes or, in theabsence of local codes, the latest edition of the National Fuel Gas Code ANSI Z223 - 1. Copiesof ANSI Z223 - 1 are available from the American Gas Association, 8501 East Pleasant ValleyRoad, Cleveland (Independence), Ohio 44131.

FOR YOUR SATISFACTION

When installing this appliance readthese instructions carefully.

Be sure that the water and gaspressures required (See Page 4) areavailable

Be sure that the water flow throughthe appliance is correct (See Page 14).

WINTER DRAIN DOWN

If the appliance is to be left infreezing conditions it must bedrained using the procedureshown on Page 16 - Winterization.

WarningCalifornia Proposition 65 lists chemical substances known to the state to cause

cancer, birth defects, death, serious illness, or other reproductive harm. Thisproduct may contain such substances be their origin from fuel, fuel combustion,

(gas/oil), or components of the product itself.

3Part No. 27/19243

ContentsPage Page

All Models

Important Requirements................................................2Information & Specifications..........................................4

CF Models

Specific Requirements...................................................5Dimensions & Clearances..............................................6Installation.................................................................7

DV Models

Specific Requirements...................................................8Dimensions & Clearances..............................................8Installation.................................................................9

All Models

Water Lines..................................................................11

Gas Lines.....................................................................12

Lighting Instructions.....................................................13

Setting the Flow Rate....................................................14

All Models Continued..

Annual Maintenance.........................................................15

Winterization Procedure...................................................16

Servicing..............................................................17

1. General Access......................................................172. To Remove Controls Tray......................................183. To Remove Burners...............................................194. To Clean the Burner................................................195. To Remove the Thermocouple...............................196. To Remove Spark Generator.................................207. To Remove Spark Electrode..................................208. To Remove Water Diaphragm................................219. To Remove Pilot Injector & Pilot Filter......................2210. To Remove Burner Manifold...................................2211. To Remove Automatic Valve Assembly..................2312. To Remove the E.C.O. Assembly...........................2313. To Remove Thermostat.........................................2414. To Remove Heating Unit........................................25

Trouble-Shooting..............................................................26

Spare Parts.......................................................................30

The Myson CF 325 The Myson DV 325

Contents

Fig. 1

4 Part No. 27/19243

Technical Specifications

Nominal Heat Input 20,000 Btu/hr Minimum - 100,000 Btu/hr MaximumTemperature Adjustment Automatic (90 Deg. F Rise, Max. Temp. 140 Deg. F)Gas Type Natural or Propane (SPECIFY GAS TYPE)Nominal Burner Manifold Pressure Nat. Gas0 - 2,000ft (0 - 610m) 4.3" W.C.Nominal Burner Manifold Pressure LP. Gas0 - 2,000ft (0 - 610m) 9.3" W.C.Maximum Gas Inlet Pressure - Nat. Gas 10.5" W.C.Maximum Gas Inlet Pressure - LP. Gas 13.0" W.C.Min. Inlet Nat. Gas Pressure 6" W.C.Min. Inlet LP Gas Pressure 11" W.C.Recovery Time 101 GAL/Hour @ 90.0F RiseThermal Efficiency 78.5%Volume 1/2 GallonETL Lab, First Hour Rating 113.6 GallonsEnergy Factor .64Pilot Standing Pilot, Piezo Ignitor, Energy: 308 Btu/Hr.Minimum Flow To Activate 3/4 Gallons Per MinuteWater Connections 3/4" Male N.P.T.Gas Connections 3/4" Female N.P.T.Water Pressure Optimum Operating Pressure 35 - 50 PsiMaximum Water Pressure 150.0 Psi

THE MINIMUM OPERATING HEAD THROUGH THE APPLIANCE IS 25ft (11 lb.f/in) AT A NOMINAL WATER RATE OF1.9 gal/min. AND ANY OTHER PRESSURE LOSSES INCURRED THROUGH THE ADDITION OF EXTERNAL PIPESAND FITTINGS MUST BE TAKEN INTO ACCOUNT ON INSTALLATION.

Flow Rates

50 Temperature Rise - 3.00 Gallons per Minute 180.0 Gallons per Hour70 Temperature Rise - 2.15 Gallons per Minute 129.0 Gallons per Hour90 Temperature Rise - 1.68 Gallons per Minute 101.0 Gallons per Hour

Vent Sizes & Direct Vent Options

CF 325 NG/LP 5.0" Standard Type B VentDV 325 NG/LP 12" x 12" Wall OpeningDVK48 Vent Kit Telescopic (Standard) 6" Min. -10" Max. Wall ThicknessDVEXT (Optional for DV) 4" Min. - 24" Max. Wall ThicknessDVPWP (Optional for DV) Required when exterior wall is any material other than masonry.DVFZK (Optional for DV) Heat Exchanger Freeze Protection Kit

Freeze Kit Requires 110VAC and is not a warranty againstfreezing.

Information & Specifications - All ModelsThe Myson 325 series is a wall mounted gas appliance that delivers a continuous supply of hot water on demand. The Myson325 easily connects directly to your cold water inlet and hot water outlet. When your shower or faucet is opened, 14 powerfulburners instantly heat your water as it passes through an all copper heat exchanger.

Unlike the tank-type water heater that wastes energy by keeping water hot all the time, the Myson 325 instantaneously heatsCOLD WATER IN ...HOT WATER OUT so you can continuously use hot water up to its actual capacity. At normaltemperatures this translates to the 2 - 3GPM range, or being able to operate one major fixture (shower/tub) at a time.

Information & Specifications

5Part No. 27/19243

CF Models - Specific RequirementsAppliances Located in Unconfined Spaces

An unconfined space is one whose volume is not less than 50 Cubic Feet per 1,000 Btu Hour, of theaggregate input rating of all appliances installed in that space. Rooms communicating directly with the spacein which the appliances are installed, through openings not furnished with doors, are considered a part ofthe unconfined space. This will allow enough infiltration of fresh air for the purpose of combustion of the gas,ventilation and dilution of the flue products. Any area not complying with the above size requirement isconsidered a confined space. Therefore a confined space is any space whose volume is less than 50 CubicFeet per 1,000 Btu Hour of the aggregate input rating of all appliances installed in that space. However, inbuildings of tight construction (for example Weatherstripping, Heavy Insulated, Caulked, Vapor Barrier,etc.), there is a need to take air from outside the building for either confined or unconfined spaces - SeeSection below "All Air from Outside the Building".

Appliances Located in Confined Spaces (All Air from Inside the Building)The confined space shall be provided with two permanent openings, one commencing within 12" of the topand one commencing within 12" of the bottom of the enclosure. Each opening shall have a minimum freearea of 1 square inch per 1,000 Btu Per Hour of the total input rating of all appliances in the enclosure. Underno circumstances should the total free opening be less than 100 square inches.

Appliances Located in Confined Spaces (All Air from Outside the Building)The confined space shall be provided with two permanent openings, one commencing within 12" of the topand one commencing within 12" of the bottom of the enclosure. Each opening shall have a minimum freearea of 1 square inch per 1,000 Btu:-

4,000 Btu Per Hour input rating of all appliances in the enclosure if the opening is through a direct openingor through a vertical duct.2,000 Btu Per Hour input rating of all appliances in the enclosure if the opening is through horizontal ducts.

Note that any air ducts must have the same or larger cross section size as the opening they feed andrectangular ducts must not be less than 3" in any direction of the cross section.

The appliance must be located as close as practicable to a chimney or gas vent.

Vent Installation

This appliance shall be connected to a 5" dia. vent. The pitch must be upwards from the appliance and theslope must comply with ANSI Z223-1.

If the appliance is to be fitted onto a combustible wall, the appliance shall be connected to either, a B1 gasvent connector or the combustible wall be protected as outlined in ANSI Z223-1.

This appliance shall not be installed in bathrooms, bedrooms, or any occupied rooms normallykept closed.

Operation of exhaust fans, kitchen ventilation systems, clothes dryers, or fireplaces may createconditions requiring special attention to avoid unsatisfactory operation of installed gasappliances.

CF Models - Specific Requirements

6 Part No. 27/19243

CF Models - Dimensions & Clearances

CF Models - Dimensions & Clearances

Fig. 2

Minimum Clearancesfrom combustible or non-combustible construction,2 inches sides, 0 inchesback, 13 inches top and 6inches bottom.

Minimum Clearances forInstallation, Servicing andProper Operation

Top 13"Sides 2"Bottom 9"

Height 34 1/2"Width 16 5/8"Depth 10 7/8"

Weight 56 lbs

7Part No. 27/19243

CF Models - InstallationInstallation

a) Unpack the carton, DO NOT throw awaythe packaging until the installation iscomplete.

b) Remove the two screws at the lower edgeof the Cover and lift off.

c) Make sure the appliance is level. Secure tothe wall using fasteners appropriate for thewall construction through the four holes inthe rear of the chassis.

d) Loosen the four screws (with lock washers)in the chassis base and locate the deposittrays, secure and re-tighten the four screws.

e) Connect the appliance to a 5" dia. ventpipe.

f) Go to Page 11 and carry on with theinstallation.

CF Models - Installation

Fig. 3

8 Part No. 27/19243

DV Models - Specific RequirementsExposing the heater to temperatures below 32 Degrees F. (Freezing) may result in freeze up of the heatexchanger or damage to the thermostat and possible damage to the heater. For installations in areaswhere winter temperatures drop below freezing, it is necessary to install a freeze protection kit (SeePage 4) to assist in protecting the unit against freeze up.

Correct Vent Installation

This appliance must be connected to a direct vent specifically designed for this appliance. The Myson 325 comeswith a 6" to 10" Telescopic Vent Kit as standard. For wall thicknesses over 10" a 4" to 24" Vent Kit is available as anoption.

The body of the appliance may be mounted on a wall of combustible construction. The vent assembly may go throughcombustible construction but the vent terminal when mounted on an exterior wall surface of other than masonrymaterial must be installed in conjunction with the Protective Plate Kit (See Page 4).

DV Models - Specific Requirements, Dimensions & Clearances

Fig. 4

DV Models - Dimensions & Clearances

Height 29 3/8"Width 16 5/8"Depth 10 7/8"

Weight 53 lbs

Minimum Clearancesfrom combustible or non-combustible construction,2 inches sides, 0 inchesback, 6 inches top and 6inches bottom.

Minimum Clearances forInstallation, Servicing andProper Operation

Top 2"Sides 2"Bottom 9"

9Part No. 27/19243

DV Models - InstallationSiting the Vent

When choosing a site for the vent, observe the following points:-a) The vent must be installed on an outside wall.b) The area of the wall covered by the appliance must be flat to prevent distortion of the chassis and outer cover.c) Site the vent away from obstructions, such as downspouts, overhanging eaves and balconies wherever possible. It is

strongly recommended that there be a clear space of approximately 12" on every side of the vent outlet.d) The vent should be 12" clear of any opening window.e) The vent should be positioned clear of ventilating fans.f) Precautions should be taken to protect plastic fittings i.e. guttering and downspouts from the hot products of combustion,

if sited close to the flue outlet.g) Position the vent clear of any projections, corners or alcoves on the face of the building.

DV Models - Installation

Fig. 5

Vent Installation

a) Decide on a suitable site for the ventand attach the paper template to thewall. Observe the minimumclearances shown on the template.To ensure correct removal of theouter cover a forward clearance of19" is required from the inside walldirectly outwards.

b) Cut a hole in the wall 12" square.c) Using the self tapping screws

provided attach the side brackets tothe vent.

d) Measure the overall wall thicknessand extend the terminal so that theair box is equal to the overall wallthickness. Seal all round the innertube joint using the sealant providedand seal the outer vent with sealingtape.

e) Insert the vent into the wall. Theinner plate is marked TOP. Ensurethat the fastening studs at the topare horizontal, check using a levelafter the vent is in position.Ensure that the inner plate is levelwith the face of the wall and all of themesh protrudes from the outer wallface.

f) Using the vent as a template, drillfour holes to accept wall plugs.Alternative hole positions areprovided in the side brackets ifrequired.

g) Secure the side brackets usingfasteners appropriate for the materialto which they are attached to. DONOT remove the four nuts andwashers from the vent.

h) Seal around the vent with a siliconewaterproof sealant (not supplied).Remove all traces of sealant fromthe metal faces of the vent. Ensurethat the drain holes in the outer ventare clear.

10 Part No. 27/19243DV Models - Installation

Combustible Wall Installation

A combustible exterior wall would be constructedfrom a wooden frame, wood siding, wood shingles,aluminium siding, and any wall with a combustibleexterior surface.When installing a vent into a combustible wall thecombustible wall must be suitably protected. A kit -DVPWP is available from your dealer.

Fig. 5A shows the top and side plates in position.

Fig. 6

Appliance Installation

a) Unpack the carton, DO NOT throw away thepackaging until the installation is complete.

b) Remove the two screws at the lower edge of theCover and lift off. Remove cardboard packingunder cover.

c) Install the sealing strip (Packed separately in thecarton) into the recess around the opening at theback of the appliance.

d) Position the appliance over the four mounting studs on the vent.e) Push the appliance towards the wall so the outlet duct on the appliance locates into the circular duct on the vent.f) Secure the appliance to the vent with the four washers and nuts removed at d).g) Go to Page 11 to continue with the installation.

Fig. 5A

11Part No. 27/19243 Water Lines

Water LinesAn approved pressure relief valve must beinstalled near the hot water outlet of this heater.

If a water heater is installed in a closed watersupply system, such as one having a backflowpreventer in a cold water supply line, means shallbe provided to control thermal expansion. Contactthe water supplier or a local plumbing inspectoron how to control this situation.

If the pressure relief valve discharges periodically,this may be due to thermal expansion in a closedwater system. Contact the water supplier or localplumbing inspector on how to correct thissituation.

For safe operation of the appliance, the outletdischarge of the relief device must not be plugged,restricted or reduced in any way to restrict therelieving capacity of the valve upon discharge.The relief device outlet should be connected tosuitable size tubing or piping and run to a suitableplace for disposal of hot water if discharge shouldoccur.

The lines should not restrict the flow of water andshould be so run to allow complete drainage ofthe valve and line upon discharge.

This appliance is equipped with an automaticgas shut-off/energy cut-off system actuated byhigh water temperature.

NO VALVE SHALL BE PLACED BETWEENTHE PRESSURE RELIEF VALVE AND THEHEATER.

It is recommended that isolation valves are fittedin the cold water in and hot water out lines.

The recommended pipe size for water lines is "I/D.

a) Connect the water lines to the fittingsprovided (" N.P.T. Male Pipe Threads).The cold water connection is on the righthand side.The hot water connection is on the lefthand side.

b) Open the isolating valves and open all hotwater faucets.

c) Turn the water throttle (See Fig.9) to thefull flow position and allow the water topass through the appliance. Note: Turningthe throttle counter clockwise increasesflow, clockwise decreases flow.To ensure that all air has been purged fromthe water lines, wait until water flows freelyfrom all the hot water faucets.

d) Turn off all the hot water faucets.e) Check cold and hot water lines for water

leaks.

Fig. 7

Fig. 8

Fig. 9

12 Part No. 27/19243Gas Lines

Gas LinesSome utilities now use high pressure gasdistribution gas distribution lines inside thebuilding. In these instances, an independentgas regulator must be fitted in addition to theregulator supplied with the heater.

To reduce the risk of damage to the gas unionconnection, we recommend that the pressureregulator/manual gas valve is connected to thegas supply line before connection to the heater.

The inlet pressure must not exceed the valuespecified on Page 4.

To assist in the dismantling of the heater, thegas supply line should be connected in such away to allow the pipework to drop approximately" to allow the controls tray to be removed.

Do Not overtighten the gas inlet connectionon the heater. Overtightening will damagethe F.S.D Assembly and void the appliancewarranty.

a) Connect the Gas

NATURAL GAS: Connect " I/D gas supplyline to the manual gas valve (" N.P.T. Femalepipe thread).

L.P.GAS: Connect " I/D or 5/8" I/D gassupply line to the manual gas valve (" N.P.T.Female thread).

b) Turn ON the gas supply and be sure thatthere are NO LEAKS using soap and watersolution. NEVER USE AN OPEN FLAMETO CHECK FOR GAS LEAKS.

c) Re-install the appliance cover and secureusing the two screws removed earlier.

The appliance and its individual shut-off valvemust be disconnected from the gas supplypiping system during any pressure testing ofthat system at test pressures in excess of 1/2psig (3.5kPa).

The appliance must be isolated from the gassupply piping system by closing its individualmanual shut-off valve during any pressuretesting of the gas supply piping system at testpressures equal to or less than 1/2 psig(3.5kPa).

Fig. 10

DV Models OnlyWARNING

The appliance cover of this heater is notmerely a cosmetic device. It is a functioning

component in the air supply to the burner andMUST BE replaced (and secured with screws)with great care before any attempt is made to

light the burners.

To allow the main burner to ignitewithout the case in position is a hazard.

13Part No. 27/19243

FOR YOUR SAFETY READ BEFORE LIGHTINGFOR YOUR SAFETY READ BEFORE LIGHTINGFOR YOUR SAFETY READ BEFORE LIGHTINGFOR YOUR SAFETY READ BEFORE LIGHTINGFOR YOUR SAFETY READ BEFORE LIGHTING

WARNING: If you do not follow these instructions exactly, a fire or explosionmay result causing property damage, personal injury or loss of life.

A. This appliance is equipped with a manually operatedignition device to light the pilot. Do NOT try to lightthe pilot by hand.

B. BEFORE LIGHTING smell all around the appliancearea for gas. Be sure to smell next to the floorbecause some gas is heavier than air and will settleon the floor.

WHAT TO DO IF YOU SMELL GAS Do not try to light the appliance. Do not touch any electric switch. Do not use any phone in your building. Immediately call your gas supplier from aneighbor's phone. Follow the gas supplier'sinstructions.

If you cannot reach your gas supplier, call thefire department.

C. Use only your hands to push in the control buttons.Never use tools. If the buttons will not push in byhand, don't try to repair them, call a qualified servicetechnician. Force or attempted repair may result in afire or explosion.

D. Do not use this appliance if any part has been underwater. Immediately call a qualified service technicianto inspect the appliance and to replace any part of thecontrol system and any gas control which has beenunder water.

LIGHTING INSTRUCTIONSLIGHTING INSTRUCTIONSLIGHTING INSTRUCTIONSLIGHTING INSTRUCTIONSLIGHTING INSTRUCTIONS

1. STOP ! Read the safety information above.

2. Turn OFF all hot water outlet faucets.

3. Open the manual gas control valve.

4. Turn OFF gas by pressing and releasing the left hand button .

1. Press the OFF button . Do not force.2. Should overheating occur or the gas supply fail to shut-off, turn off the manual gas control valve to the

appliance.

TO TURN OFF GAS TO APPLIANCETO TURN OFF GAS TO APPLIANCETO TURN OFF GAS TO APPLIANCETO TURN OFF GAS TO APPLIANCETO TURN OFF GAS TO APPLIANCE

6. Find Pilot. The pilot can be observed through thepilot viewing window on the appliance cover.

7. Fully depress the Starter/Pilot Button andhold in until the air is purged from the system. Allthe air must be purged from the system before thepilot will ignite, this may take 2 - 3 minutes.

8. Repeatedly press and release the Spark IgnitionButton until the pilot is lit. Keep the Starter/Pilot Button depressed for 10 seconds after thepilot is lit then release, the pilot should remain lit.If the pilot goes out repeat steps 1 to 8.If pilot will not stay lit after several tries, call yourservice technician or gas supplier.

9. Press down the Full Gas Lever to release the Starter/Pilot Button. The button will pop out towards you.The appliance is now in the working position andwill supply hot water when a hot water faucet isopened.If the button does not pop out when the lever ispressed, STOP and immediately call your servicetechnician or gas supplier.

10.The appliance can be returned to the pilot onlyposition at any time by depressing the Starter/PilotButton.

5. Wait five (5) minutes to clear out any gas. If you thensmell gas, STOP! Follow B in the safetyinformation above.If you don't smell gas, go to the next step.

Lighting Instructions

Fig. 11

14 Part No. 27/19243

Setting the Flow Rate

BE SURE THAT THE CUSTOMER HAS A FULL EXPLANATION OF THE APPLIANCE.

IN HARD WATER AREAS, OUTLET WATER TEMPERATURES IN EXCESS OF 140F MAY RESULT IN SCALEFORMATION.

Setting the Flow Rate

a) Press the 'OFF' Button to turn off theheater. The pilot light will go out.

b) Fully open the furthest Hot water outletfaucet and adjust the water throttle to giveat least 2.4GPM (which takes 6.2 secondsto fill a quart measure).

c) Turn OFF the hot water outlet faucet.

d) Remove the burner manifold pressure testpoint screw and attach a manometer.

e) Re-light the pilot and set to full gas.

f) Check the gas pressure reading againstthe values stated on Page 4. If the gaspressure is below this value refer to thetroubleshooting section starting on Page26.

IF THE BURNER MANIFOLD PRESSUREIS LOW, THE OUTLET WATER

TEMPERATURE WILL BE REDUCED.

g) Fully open a hot water outlet faucet. Thenre-adjust the water throttle (Fig.9.) to give2GPM (which takes 7.5 seconds to fill aquart measure).Note: Same as Page 11, c.

h) Check outlet water temperature, thetemperature should be between 130Fand 140F. If the temperature is below130F refer to the troubleshooting sectionstarting on Page 26.

j) Press the 'OFF' button to turn off the heater.Remove the manometer and re-install theburner manifold pressure test point screw.

k) Install the control cover.Approximate time to fill a measure.

Quart Measure - 7.5 SecondsHalf Gallon Measure - 15 SecondsOne Gallon Measure - 30 SecondsFig. 12

CAUTION

WATER TEMPERATURES ABOVE 140F INCREASETHE RISK OF SCALD INJURY

15Part No. 27/19243

Annual MaintenanceTo ensure continued safe and efficient operation of this water heater, it is recommended that it is checked and serviced asnecessary at regular intervals. The frequency of servicing will depend upon the particular installation conditions and usage,but in general once a year should be adequate.

Note: In hard water areas, scale may build up on the push rod, seals and on the inside of the underside housing of thediaphragm housing. They may require regular descaling. Scaling problems (excessive mineral build-up) usually occur intank-type heaters. Because MYSON heaters do not store hot water, and because constant flow through the unit tendsto flush the heat exchanger, scaling should not be a serious problem. Since MYSON heaters are designed for many yearsof use, however, if descaling is required contact your local dealer.

Annual Maintenance

Fig. 13

Examine the venting system, clean and repair asnecessary.Examine the pilot and burner flames, they should burnwith a blue flame. Some yellow is acceptable with L.P.GasAt least once a year do a manual operation of thepressure relief valve.Before operating the pressure relief valve, shut downthe appliance, open a hot water faucet and allowwater to run until it is cold. Close the faucet thenoperate the pressure relief valve. Protect the areafrom damage by water with a suitable container.

Operate the appliance noting any problems in thecomponents. Carry out the annual maintenanceprocedure then correct any other faults by referring tothe servicing section in which you will find details onhow to replace parts.

Check the burner ignition is smooth and quiet when ahot water faucet is opened.The burner ignition has been factory set and shouldnot need adjustment, however, if adjustment is requireda slow ignition screw is fitted to the heater and islocated as shown in Fig 15. Turning the screwclockwise delays the ignition, counter-clockwiseadvances the ignition. When correct, burner ignitionshould be smooth and quiet.

DV Models: WARNINGNever Operate this Heater with the Appliance

Cover Removed.

a) Check the piezo unit, flame safety device andthermocouple, clean or replace if necessary.

b) Remove the burner assembly and clean using asoft brush or vacuum cleaner.

c) Check the pilot injector and clean or replace ifnecessary.

d) Remove the diaphragm housing and gas valvecomplete with push rod. Replace the seals ifnecessary. Descale and regrease the push rod,washers and diaphragm housing using a siliconegrease.

e) Remove the thermostat assembly. Descale andregrease using a silicone grease.

f) Check for water and gas leaks. Replace 'O' rings,sealing washers and gaskets where required.

g) Clean any deposits off the heating unit by washingor brushing. Descale the heating unit if required.

16 Part No. 27/19243

Winterization ProcedureShut-Down Procedure

a) Shut off gas supply.

b) Shut off cold water supply.

c) Open pressure relief valve, hot water faucet,and leave open.

d) Disconnect hot water outlet and cold waterinlet.

e) Remove drain plug from the bottom of thediaphragm cover and leave out.

f) Loosen 3/4" brass nut on the thermostatbulb at top right of heat exchanger andjiggle to loosen 'O' ring seal, allowing air intothe heat exchanger. Leave open.

g) Loosen 3/4" brass nut on bottom ofthermostat assembly, pull the pipe downslightly and leave unattached.

Start-Up Procedure

a) Lubricate thermostat bulb and 'O' ring usinga silicone grease.

b) Install the plug at bottom of diaphragmcover.

c) Check cold water inlet screen for debris andconnect both cold and hot waterconnections.

d) Open hot water faucet. Slowly turn on coldwater until all air is removed and waterfollows through the heater. Check for leaks.

e) Re-light the pilot. For pilot lightinginstructions, see inside bottom control cover.

Winterization Procedure

Fig. 14

17Part No. 27/19243

ServicingREPLACEMENT PARTS MUST BE FITTED BY A PERSON SUITABLY QUALIFIED

IN THE MAINTENANCE OF GAS APPLIANCES.1. General Access

a) Turn Off the gas supply.

b) Turn Off the water supply.

c) Slide out the control cover.

d) Remove the two screws securing theappliance cover at the lower edge. Swingout the lower edge and lift off the outerCover.

e) Open a hot water faucet to reduce thepressure and drain the appliance using thedrain off point fitted on the underside of thediaphragm housing.

Servicing

Fig. 15

18 Part No. 27/19243

2. To Remove Controls Tray

a) Perform General Access - Section 1.b) Disconnect the gas regulator from the

flame safety device.c) Drop the gas supply pipe and regulator

approx. 1/2" to clear the gas inletconnection.

d) Disconnect the E.C.O connections fromthe thermocouple connector.

e) DV Only: Unscrew the union nutsecuring the pressure test pointextension tube to the chassis.

f) Loosen, but do not remove, the two nutssecuring the tray to the chassis.

g) Remove the screws and yokes securingthe sensing tubes.

h) Pull the sensing tubes clear from thethermostat valve assembly anddiaphragm housing, taking care not tolose the 'O' rings.

j) Holding the controls tray securely,remove the two nuts together with theirscrews and washers.

k) Remove the complete controls/burnerassembly tray by pulling carefullyforwards and slightly downwards.

l) When re-installing, ensure that thewashers are correctly positioned underthe screw heads and that the sensingtubes are correctly positioned.

Servicing

Fig. 16

Fig. 17

Fig. 18

19Part No. 27/19243

3. To Remove Burners

a) Perform General Access and remove theControls Tray - Sections 1 & 2.

b) Remove the two screws as shown andcarefully remove the heat shield.

c) Carefully remove the burner bars, startingfrom the ends and working inwards.

d) The air guide plate will be loose on removalof the burner bars.

e) On re-assembly, ensure that the burnersare correctly fitted to the injectors and frontlocation points.

4. Cleaning the Burner

During the annual cleaning of this appliance,the burners should be checked to see thatthere is no scale or foreign material blockingthe burner ports. The burners can also becleaned by removing the burner tray assemblyand using a vacuum cleaner to remove theforeign material.

5. To Remove the Thermocouple


b) Remove the four center burner bars.c) Disconnect the split nut from below the

thermocouple in the pilot block.d) Disconnect the nut at the other end of the

thermocouple.e) Pull the thermocouple probe down to clear

the pilot block and remove.f) Re-install in reverse order. Ensure the

thermocouple is pushed right up inside thepilot block.

A replacement thermocouple,Part No. 10-13848 is available

from your dealer.

Servicing

Fig. 19

Fig. 20

Fig. 21

20 Part No. 27/19243

6. To Remove Spark Generator

a) Slide out the control cover.b) Disengage the electrode lead from the

spark generator.c) Remove or loosen and pull aside the spark

button retainer, taking care not to lose theshakeproof washer.

d) Pull off the button and unscrew the sparkgenerator unit from its housing.

A replacement Spark Generator,Part No. 10-11935 is available

from your dealer.

7. To Remove Spark Electrode


b) Remove the four center burner bars.c) Disengage the electrode lead from the

rear of the spark generator.d) Disconnect the split nut from below the

thermocouple in the pilot block.e) Lift the pilot block clear of the pilot tube

(loose fit).f) Remove the screw securing the electrode

to the pilot block.g) Pull the electrode lead through the rubber

grommet to clear the controls tray.

A replacement Spark Electrode,Part No. 10-12259 is available

from your dealer.

Servicing

Fig. 22

Fig. 23

Fig. 24

21Part No. 27/19243 Servicing

8. To Remove Water Diaphragm


b) Remove the screw and yoke securing thesensing tubes to the water diaphragm.Do not lose the 'O' rings.

c) Lay controls assembly on its burners withthe diaphragm housing facing up.

d) Remove the eight screws and separate thediaphragm cover from its housing.

e) Remove the diaphragm.f) Place the diaphragm centrally into the

housing with the metal plate on thediaphragm against the push rod.g) Be sure that the two 'O' rings in the cover

are correctly positioned (a small amount ofsilicone grease can be used to hold the 'O'rings in place).

h) Place the cover carefully in position abovethe diaphragm.

j) Insert the eight screws and secure fingertight, check that the diaphragm has notslipped out of its seating.Care must be taken when securing thehousing to make sure that the diaphragmis correctly located.Failure to do so may cause the unit to leakand can result in permanent damage to thediaphragm.

k) Secure all eight screws in the order shown.l) Ensure that the sensing tubes are correctly

fitted.m) Re-assemble the appliance and check for

leaks.

A replacement Diaphragm Assembly,Part No. 10-12460 is available

from your dealer.

Fig. 25

Fig. 26

Fig. 27

22 Part No. 27/19243

9. To Remove Pilot Injector & PilotFilter


b) Release the union nut at the base of thepilot tube. Remove the heat shield ifnecessary.

c) Raise the pilot feed tube and push towardsthe back of the appliance.

d) Remove the pilot injector from the bottomof the tube.

e) Clean the injector orifice by blowing throughwith air. Do not put any foreign objectthrough the orifice.

f) When re-assembling ensure that the pilotinjector is correctly positioned.

g) Remove the pilot filter body and tap out thepilot filter, clean and re-install as required.

A replacement Pilot Tube Assembly,Part No. 10-12872 (N.G.) - 10-12873(L.P.G.) is available from your dealer.

10. To Remove Burner Manifold


b) Remove all burner bars and the air guideplate.

c) DV Only: Unscrew the union securing thepressure test point extension tube to theburner manifold.

d) Remove the three screws securing theburner manifold to the automatic valve - liftoff the burner manifold.

e) Replace the manifold gasket if necessarybefore re-assembly.

Servicing

Fig. 28

Fig. 29

Fig. 30

23Part No. 27/19243

11. To Remove Automatic ValveAssembly


b) Remove the burner bars and burnermanifold.

c) Disconnect the union nut.d) Release the retaining plate (two screws)

and remove the burner supply pipe.e) Remove the two screws and lift away the

automatic valve.f) Check that the brass disc and push rod

seal are seated correctly in the top openingof the diaphragm housing.

j) When re-assembling, ensure that the valvepush rod is free from surface imperfectionsand is lubricated with a silicone grease.

Note: The burner supply pipe must be fittedAFTER the automatic valve so as toprevent damage to the valve push rod.

12. To Remove the E.C.O. Assembly

a) Shut down the appliance.b) Slide out the control cover.c) Pull the electrical connectors off the

thermocouple interrupter insert.d) Remove the two screws to release the

E.C.O. Assembly.e) Cut the leads to allow them to be pulled

complete with grommets out of the chassis.f) When installing the new E.C.O assembly

Do Not install the electrical connectorinsulators until the new leads completewith grommets have been passed throughthe holes in the chassis.

A replacement E.C.O. Assembly,Part No. 10-19055 is available

from your dealer

Servicing

Fig. 31

Fig. 32

Fig. 33

24 Part No. 27/19243

Caution:Water temperatures above 140F dramatically increases

the risk of scalding.

13. To Remove Thermostat

a) Perform General Access - Section 1.b) Remove the thermostat bulb from its pocket -

section 14 b).c) Remove the rubber grommet clear of the capillary

tube and base of chassis.d) Release the sensing tubes by removing the screw

and yoke. Take care not to lose the 2 'O' rings.e) Remove 1 screw and lockwasher and separate

the thermostat valve assembly from the throttlebody, taking care not to lose the 'O' rings betweenthe assemblies.

f) Carefully pull the thermostat valve assembly downand forwards to clear the chassis.

g) Remove the 2 long screws to detach the thermostatand spacer.

h) When re-installing ensure that the spacer iscorrectly located between the thermostat flangeand the retaining plate.Note: The retaining plate must be fitted with itsdrain hole at the bottom relative to the wholeappliance.

j) Check that the 2 'O' rings are in position betweenthe thermostat valve assembly and the throttlebody before securing with the screw.

k) Dismantle, clean and re-grease with a siliconegrease. Re-assemble in reverse order.

l) When re-installing the thermostat bulb ensurethat the 'O' ring in the bulb housing is correctlyseated - see section 14.

m) Ensure the sensing tubes are correctly fitted.n) Check that the operation of the thermostat is

between 130F and 140F.

Servicing

Fig. 34

Fig. 35

Fig. 36

IMPORTANT

After Service, Check & Re-Calibrate theThermostat

a) Attach a manometer to the burner pressuretest point.

b) Light the pilot and press the 'Full Gas' lever.c) Open a hot water faucet to full flow, and open the

water throttle (over 2 GPM required). Very slowly,allowing the thermostat to follow adjustments,reduce the water flow at the water throttle until a0.25" w.c. reduction in burner pressure occurs. Atthis point, the thermostat has just started to controlthe gas valve.

d) Measure the outlet water temperature, it shouldbe approximately 130F - 140F. If not use anallen wrench to adjust the allen screw on the frontof the body (Clockwise increases the temperature,counter-clockwise reduces the temperature). Aftereach adjustment, go back to c) to re-check thetemperature.

e) After any adjustment check all the hot wateroutlets. Once the outlet temperature is correct,the water flow will also be correct.

25Part No. 27/19243 Servicing

14. To Remove Heating Unit

a) Perform General Access - Section 1.b) Remove the thermostat bulb from its

pocket.

CAUTION: To prevent possible damage tothe heating unit, loosen the split nut whilesupporting the bulb housing hexagon boss.

c) Release the two union connections atthe base of the chassis.

d) Remove the four screws securing theheating unit to the chassis.

e) Carefully pull the heating unit forwardsfrom the top and lift.

f) Remove the down draft diverter/primaryflue by unscrewing the four screws (twofront and two rear).

Note: On re-assembly, ensure that the 'O'ring in the thermostat bulb housingis properly seated.

IMPORTANT:Before re-installing the down draft diverter

(CF)/primary flue (DV), remove and discardthe sealing gasket and fit a new one -

Part No. 10/10916.

g) When installing the new sealing gasket,the adhesive side attaches to the downdraft diverter (CF)/primary flue (DV). Agood seal all round between the downdraft diverter/primary flue andcombustion heat exchanger must beachieved to ensure correct performance.

Fig. 37

Fig. 38

26 Part No. 27/19243

Trouble-Shooting

SYMPTOM POSSIBLE CAUSE SOLUTION

1. Turn on the gas at the manualgas valve and/or the main gasline. At tank on LPG gas supply.

2. Purge the air line by depressingand holding the center 'Pilot/Start'button, this may take 2-3 minutes.

3. Follow the lighting instructionslocated on the control cover orrefer to these instructions.

4. Re-connect the electrode lead.

5. Adjust the spark gap. The gapbetween the electrode tip and thepilot hood should be 1/8".

6. Check the electrode lead is routedclear of all metal parts.

7. Clear injector by blowing throughor replace with pilot tube assy PartNo 19-12872 Nat Gas or Part No19-12873 L.P.G.

8. Replace any faulty componentsfound. Piezo Unit - Part No 10-11935. Electrode Assembly - PartNo 10-12259.

9. Call in your gas supplier.

Pilot Will Not Light 1. Gas not turned on.

2. Air in gas line.

3. Incorrect pilot lighting procedure.

4. Electrode lead not connected tothe rear of the spark igniter.

5. Incorrect spark gap.

6. Electrode lead grounded out.

7. Pilot injector blocked.

8. Faulty components.

9. No gas to the appliance.

Trouble-Shooting

Pilot Lights But Does Not RemainLit

1. Thermocouple connections loose.

2. E.C.O. connections may be loose.

3. Pilot flame 'soft' or too small toheat the thermocouple tip.

4. Thermocouple worn out ordamaged.

5. Faulty magnet unit in the flamesafety device.

6. E.C.O. Failure

1. Tighten the connections.

2. Clean/Replace and checkconnections are tight.

3. Pilot injector partially blocked,clear by blowing through orreplace. Check the gas inletpressure is correct - see Page 4.

4. Replace the thermocouple - PartNo 10-13848.

5. Replace magnet - Part No10-14774.

6. Diagnose by shorting out, replaceif diagnosis is correct. Do not delay,this is a safety device.

27Part No. 27/19243

SOLUTIONPOSSIBLE CAUSESYMPTOM

PPPPPilot Lit But Main Burner Will NotLight On Water Flow

1. Full gas off.

2. Gas inlet pressure low.

3. Low water flow caused by blockedwater screen or closed waterthrottle.

4. Faulty diaphragm.

5. Automatic gas valve push rodjammed.

6. Slow ignition screw incorrectly set.

7. Incorrect water pressure.

1. Depress full gas lever.

2. Call in your gas supplier.

3. Clean the debris from the screenor reset water throttle.

4. Replace the diaphragm Assembly- Part No 10-12460.

5. Dismantle clean and regreaseusing silicone grease. Handle thepush rod with care, do not bend.

6. The slow ignition screw ispositioned above the sensingtubes in the water diaphragmhousing. Turning the screwclockwise delays the ignition,counter-clockwise advances theignition. Never turn the screw fullyclockwise. When correct theburner ignition should be smoothand quiet when a hot water faucetis opened.

7. Constant water pressure shouldbe 30+ P.S.I.

Trouble-Shooting

No Or Low Water Flow Rate 1. Blocked water screen.

2. Heat exchanger blocked with lime.

3. Loss of service water mainpressure.

4. Water throttle closed.

1. Clean the debris from the screen.

2. Descale or replace - Part No10-14689.

3. Contact your water supplier.

4. Reset the water throttle.

High Water Flow Rate

See Low Water Temperature


2. Replace thermostat assembly -Part No 10-13486.

1. Automatic gas valve push rodsticking.

2. Thermostat bellows perforated.

High Water Temperature

1. Water throttle open to far. 1. Reset the water throttle.

28 Part No. 27/19243


Low Water Temperature 1. Check gas inlet pressure.

2. Replace the diaphragm assembly- Part No 10-12460.


4. The slow ignition screw ispositioned above the sensingtubes in the water diaphragmhousing. Turning the screwclockwise delays the ignition,counter-clockwise advances theignition. Never turn the screw fullyclockwise. When correct theburner ignition should be smoothand quiet when a hot water faucetis opened.

5. Replace thermostat assembly -Part No 10-13486.

6. Constant water pressure shouldbe 30+ P.S.I.

7. Reset the water throttle.

1. Gas pressure too low.

2. Tear in diaphragm.

3. Automatic gas valve push rod sticking.

4. Slow ignition screw incorrectly set.

5. Freeze/Corrosion damage tothermostat bulb.

6. Incorrect water pressure.

7. High water flow rate.

.

Trouble-Shooting

1. Check heat exchanger for scaledeposits. Ultimately this will causethe heat exchanger fins to discolorand buckle.

2. Noisy ignition could be caused byincorrect setting of the slow ignitionscrew.

3. Burner aeration ports and mainflame ports blocked.

4. Blocked pilot injector.

Noisy Heater 1. Descale or replace - Part No10-14689.

2. The slow ignition screw ispositioned above the sensingtubes in the water diaphragmhousing. Turning the screwclockwise delays the ignition,counter-clockwise advances theignition. When correct the burnerignition should be smooth and quietwhen a hot water faucet is opened.

3. Carefully clean the burners with avacuum cleaner.

4. Clean or replace pilot tubeassembly.

29Part No. 27/19243 Trouble-Shooting


Sooting 1. Check gas inlet pressure.

2. Check if appliance is NG. or LPG.

3. Check condition of seals andreplace if necessary.

4. Check the vent is installedcorrectly, See Page 9.

5. For installations above 2000ftcontact your dealer.

1. Incorrect gas pressure.

2. Wrong type of gas.

3. DV Only: Faulty seals on appliance tovent and appliance case.

4. DV Only: Vent kit not fitted correctly.

5. High altitude installation.

1. Check and rectify any faults.

2. Tighten, check DV cover and flueseals.

3. Replace thermostat bellows.

1. Vent pipe may be blocked.

2. Cover loose (DV Model).

3. Thermostat bellows perforated.

Odors(Smell of Combustion Products)

(Smell of Ether/Alcohol)

30 Part No. 27/19243Spare Parts

Spare Parts

Fig. 39

31Part No. 27/19243 Spare Parts

Replacement Parts are available from: See Back Cover for Address.

Ref Part DescriptionNo. No.

1 10/12212 Union Nut, Heat Exchanger2 10/12213 Comp. Flange, Brnz. Heat Exchanger3 20/10047 'O' Ring - Heat Exchanger4 10/13843 Outlet Adaptor, ECO @ HX5 10/12731 ADP Assembly In/Out6 10/10062 Direct Vent Flu Seal7 10/10916 Heat Exchanger Seal8 10/14689 Heat Exchanger9 10/10075 Direct Vent Case Seal10 10/19030 DV Cover - White11 10/13056 CF Cover - White12 10/19224 CF Bottom Cover - Grey

10/19226 DV Bottom Cover - Grey13 10/19055 ECO Assembly With Leads

From Serial No. 15 000 000 014 10/13849 Thermocouple Connector15 10/13846 Interrupter Insert16 10/13848 Thermocouple17 12/13055 Fix/nut Thermocouple18 22/13059 Pilot Mounting Assembly19 10/12872 Pilot Tube Assembly - NG

10/12873 Pilot Tube Assembly - LP Gas20 10/12259 Electrode Assembly21 10/12694 Pilot Filter22 10/13706 FSD Assembly23 10/12410 Magnet. Main Gas Valve24 10/11935 Piezo Ignitor25 10/13008 Regulator Assembly - NG

10/12989 Regulator Assembly - LP Gas26 10/14639 Button - Stop27 10/13705 Button - Start28 10/14641 Button - Ignitor29 10/13486 Thermostat Bellows and Bulb30 20/14834 'O' Ring - Thermostat Sensing Bulb31 10/14536 Thermostat Assembly Complete32 10/11904 Pin, Stat Assembly33 10/14637 Cold Inlet Throttle34 10/12284 Cold Water Inlet Screen35 20/12335 'O' Ring - Sensing Tube36 10/13495 Long Sensing Tube37 10/14923 Short Sensing Tube38 10/13561 Diaphragm Housing Assembly39 10/12460 Diaphragm EPDM W/Plate40 20/15360 'O' Ring - Ball Disk41 10/12373 Pin, Automatic Valve Assembly42 20/11822 'O' Ring - Diaphragm Drive Pin43 10/12458 Automatic Valve Assembly - NG

10/12803 Automatic Valve Assembly - LP Gas44 10/12848 Manifold Gasket45 10/12345 Stainless Burner46 19/12780 Standard Orifice/Inj. - NG

19/12782 Standard Orifice/Inj. - LP Gas

Manufactured by:Potterton Myson Ltd..Wyre Street, Padiham, Lancashire, England.

For Sales, Service and Parts Contact:-

McNeely - Yuill CorporationMYSON "Tankless" Gas Hot Water Heaters9911 Horn Road, Suite "100"Sacramento, California 95827. Telephone 916/362 - 1671 TeleFax 916/362 - 1698

This leaflet is accurate at the date of printing but will be superseded and should be disregarded if specifications and/or appearance are changed in theinterests of continued improvement.

Myson 325 Tankless manual

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