22
4. Overheat Thermostat.
See Fig. 34.
Check that the electricity supply to the appliance is turned off.
Remove the inner casing cover as described in Section 15.3, b.
Carefully pull off the two wires from the thermostat head.
Undo the two M3 screws and remove from the appliance.
Fit the replacement thermostat in the reverse order ensuring that
some heat sink compound is between the thermostat and the
plate.
5. Gas to Water Heat Exchanger.
See Fig. 34.
Check that the electricity supply to the appliance is turned off.
Drain the central heating circuit as described in Section 16.3, a.
Remove the inner casing cover, fan, flue hood assembly, overheat
thermostat, central heating sensor, burner and automatic air
vent assembly as described in Sections 15.3, b, e, f, and h,
16.4, 1, 16.4, 3 and 16.4, 12.
Slacken the two screws to remove the two retaining brackets and
lift the heat exchanger from the casing. Take care that the rear
insulation pad does not drop forwards onto the burner.
Fit the replacement heat exchanger in the reverse order ensuring
that both the “O” rings are correctly fitted and lubricated and a
layer of heat sink compound is on both the thermostats.
Open the valves and fill and re-pressurise the system as
described in Section 13.2.
6. Combustion Chamber Insulation. Refer to Fig. 35.
Check that the electricity supply to the appliance is turned off.
Drain the central heating circuit as described in Section 16.3, a.
Remove the inner casing cover, fan, flue hood assembly,
burner, and Gas to Water heat exchanger as described in
Sections 15.3, b, e and f, and 16.4,5. Remove the fibre
insulation pads from the combustion chamber side, rear, and
front sections. To avoid the risk of fine particles dampen the
pads before removal.
Fit the replacement pads in the reverse order taking care not to
damage them.
Open the valves and fill and re-pressurise the system as
described in Section 13.2.
7. Burner.
See Fig. 32.
Check that the electricity and gas supplies to the appliance are
turned off.
Remove the burner assembly as described in Section 15.3, h.
Fit the replacement burner in the reverse order taking care not to
damage the electrode leads.
8. Burner Injector.
See Fig. 32.
Remove the burner as described in Section 15.3, h.
Unscrew the brass injector from the burner.
Fit the replacement injector in the reverse order.
9. Spark Electrode Assembly.
See Fig. 32.
Remove the combustion chamber front and sides as described in
15.3, g.
Carefully pull off the two electrode leads,
Undo the M4 extended nut and remove the spark electrode
assembly from the burner.
Fit the replacement electrode in the reverse order, checking that
the spark gap is 3 to 4mm.
Fig. 34. Gas to water heat exchanger.
Auto air vent
Gas to water heat
exchanger
Retaining
clips
Retaining
bracket (2)
Retaining
screws (2)
Overheat
thermostat
Retaining
screws (2)
C.H.
sensor
Fig. 35. Combustion Chamber Insulation
Combustion chamber front and
side assembly
Side insula-
tion
pad
Side insula-
tion
pad
Front insulation pad
When reassembling ensure these
locations are correctly fitted in the
slots at the rear of the inner casing
View from inside the combustion chamber
Fig. 33. Air pressure switch.
Support Bracket
Red sensing tube
+ ve
Clear sensing tube
— ve
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