Flow / Return Sensor; Temperature Limiter; Replacement Of Failed Components - Hamworthy Wessex Modumax 100 series Installation, Comissioning And Servicing Instructions

heat exchanger to casing sealing gasket and fit the new
gasket previously hung on the lifting eye. Clean mating
surfaces of the heat exchanger tube header castings
and cover plates. Re-assemble the heat exchanger
assembly using new gaskets (a light coating of grease
applied to gasket faces will assist seal).
Refit heat exchanger ensuring correct rotational
orientation, so that the water connection nipples and
safety valve pipe pass through the holes in the rear of
the casing, fastening in place with the 6 M10 nuts. Refit
the water connection and safety valve pipe sealing
plates, renewing all gaskets and o-rings. Reconnect the
system pipework and check for soundness.
Ensure that the cover plates are re-fitted in the correct
orientation. Evenly torque the bolts and nuts to 7kg m.
Re-fit the burner assembly. Test all gas joints broken
or disturbed for soundness before firing.
Refer to Section 8 Commissioning The Boiler, for
correct procedures.

11.0 REPLACEMENT OF FAILED COMPONENTS

There are a number of components listed below which
can be replaced simply and quickly by following the
given procedure. In each case the operation of each
replaced component must be checked by carrying out
the appropriate part of the commissioning procedure.
See Section 8: COMMISSIONING & TESTING.
Note:- Isolate all electrical supplies to the boiler
module before removing the front cover and
commencing any
exchange procedure.
removed, turn off the gas supply at the service
valve.
11.1 Hot Surface Igniter and Flame Probe Assembly
Part Nos. 563801019 & 533805019
Note:- The igniter and flame probe ceramics are
very fragile.
Unplug the igniter from the harness, remove the single
socket cap head screw securing the igniter to the burner
flange and withdraw the igniter. When fitting the
replacement carefully feed the igniter through the
mounting hole and secure with the socket cap head
screw.
Disconnect the flame probe lead, remove the single
socket cap head screw securing the probe to the burner
flange and withdraw the probe. When fitting the
replacement carefully feed the probe through the
mounting hole taking care not to damage the ceramic.
Note:- Do not remove both securing screws at the
same time as the separate flange and Mica sight glass
will become detached.
HAMWORTHY HEATING LTD
servicing or component
With the front cover
WESSEX MODUMAX 100 SERIES
Ensure the positions of the igniter and probe are as
recommended in Figure 10.2.

11.2 Flow / Return sensor

Part No. 533901431
The two identical sensors are located in pockets on the
flow and return pipes at the rear of the boiler. To remove
the sensor, unplug the sensor from the harness, loosen
the M3 screw securing the sensor in the pocket and
withdraw the sensor.
Upon replacement ensure that the sensor is fully
engaged and secured into the pocket.
11.3 Temperature Limiter (Limit Stat)
Part No. 533901179
Check the setting of the replacement temperature
limiter, the temperature must be set at 100°C
maximum.
To replace the limiter, remove the plastic cover,
undo the shaft securing nut and withdraw the limiter
rearwards from controls fascia. Remove the electrical
connections from the temperature limiter body noting
the position of the coloured cables.
Check the operation of the replacement device by
carefully applying a heat source to the bulb. Fit the
replacement in reverse order. Ensure that the electrical
connections are replaced in the correct positions. Refer
to Figure 9.3.2 - Wiring Diagram, for details.
11.4 Gas Valve
Part No. 533903037
Note:- Some gas valve components can be replaced
without completely removing the whole assembly from
the boiler. However, Hamworthy Heating strongly
recommend that a complete new gas valve is fitted to
ensure safe, reliable operation of the boiler. Please
refer to Hamworthy Heating Technical Department
before attempting to remove components from the gas
valve.
Ensure that the boiler module electrical power and gas
supplies are isolated. Unfasten the gas valve plug
securing screws and disconnect the plug by pulling
firmly away from the valve.
Remove the 4 M5 cap head screws securing the gas
valve to the gas inlet flange, allow the flange to hang
free on the flexible gas pipe. Remove the 4 M5 cap
head screws securing the gas valve to the gas feed
pipe, taking care to support the weight of the valve. Note
that the cap head screws are different lengths at the
inlet and outlet of the valve, be sure to replace at the
correct positions.
Replace the gas valve complete with new 'O' rings,
ensuring correct orientation - gas flow is in the same
direction as the arrow marked on the valve. Replace the
gas valve leads, ensuring correct plug positions and
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