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(g)
Remove the complete union fittings from the heat bank.
Withdraw the expansion vessel. It will be necessary to slightly
displace the gas line. Protect the threads of the gas line union.
(h)
Refit the new expansion vessel after transferring the short con-
nector pipe assembly. Reassemble the appliance in the reverse
order.
(i)
Refill the system and check for the correct operation of the
controls and for the gas soundness of all relevant joints.
1 7. THE OVERHEAT THERMOSTAT
Fig. 26.
(a)
Remove the two M3 taptite screws holding the overheat
thermostat to the flow pipe.
(b)
Unscrew the limit thermostat leads from the gas valve. One is
located at the rear of the gas valve. It will be necessary to
remove the pilot pipe to gain access to the rear connection. The
connection is a hexagon nut and an M 10 open ended spanner
will be required to release the nut to allow it to be unscrewed.
(c)
Push the grommet situated in the side of the inner casing
inwards into the casing.
(d)
Thread the limit thermostat leads through into the inner casing
and remove the thermostat.
(e)
Fit the new limit thermostat connecting the lead and grommet
assembly in the reverse order. Take care not to overtighten the
rear connection. Finger tight plus a quarter of a turn is
sufficient.
NOTE. When fitting a replacement thermostat it is important
to ensure that no foreign matter is present on the contact
surfaces of both the thermostat and the mounting bracket.
During manufacture thermal grease is smeared on the
surfaces and may be left.
18. THE BOILER INNER CASING COVER SEAL
Fig. 23.
(a)
Release the six slotted hexagon head screws and washers and
remove the inner casing.
(b)
Remove the damaged sealing strip and fit the replacement
strip using silicone adhesive. Check that the strip passes
completely around the edge of the inner casing and across the
centre channel with no gaps.
(c)
Refit the inner casing and tighten the screws evenly.
1 9. THE DOMESTIC HOT WATER HIGH LIMIT
THERMOSTAT
Fig 27.
(d)
Disconnect the thermostat leads at the terminal strip Refer to
the wiring diagram (Fig
1
2) to ensure that the correct leads are
disconnected. Do not leave any leads loose in the control box.
(b)
Release the strain relief bush by compressing the loose section
of the bush and carefully withdraw the leads from the control
box.
(c)
Remove the two M3 taptite screws holding the overheat
thermostat to the flow pipe.
(d)
Fit a new thermostat and reconnect ensuring that the strain
relief bush has been replaced. Refer to the electrical wiring
diagram (Fig. 12) to ensure the correct connections are made.
NOTE. When fitting a replacement thermostat it is important
to ensure that no foreign matter is present on the contact
surfaces of both the thermostat and the mounting bracket.
During manufacture thermal grease is smeared on the
surfaces and may be left.
(e)
Re-assemble the appliance in the reverse order.
20. THE CENTRAL HEATING CONTROL THERMOSTAT
Fig 27.
(d)
Unscrew the two slotted
MS
screws located beneath the
control box and ease away the thermostat and pump delay
timer mounting bracket.
(b)
Using a pair of long nose pliers pull the retaining clip from the
thermostat pocket situated in the flow pipe and remove the
thermostat phial.
22
(c)
Remove the thermostat central clamping nut and washer.
(d)
Pull off the two electrical connections from the rear of the
thermostat.
(e)
Push the thermostat body back to disengage the spindle from
the mounting bracket.
(f)
Withdraw the thermostat and thread the capillary through the
slot in the rear of the electrical control box.
(g)
Fit the new thermostat and reassemble in the reverse order.
The capillary of the replacement thermostat must be uncoiled
to assist its passage through the control box opening with the
thermostat in position the excess capillary must be recoiled,
without tight bends and positioned so that it is beneath the
combined feed and vent pipe but not in contact with any hot
surface. Ensure that the retaining clip is replaced into the
thermostat pocket.
Fig. 25.
Schraider pressure valve
Expansion vessel
Union connection
to heat bank
Fig. 26.
Heat exchanger
Heat exchanger
union connections
Union connection
Drain cock
to expansion vessel
Combustion chamber fixing screws
I
Overheat thermostat
Combustion chamber front plate
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