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14. THE GAS VALVE
Fig. 24.
(a)
Disconnect the thermocouple from its connection at the right
hand side of the gas valve. Disconnect the pilot pipe at its entry
to the combustion chamber and at the gas valve. Remove the
pipe.
(b) Unscrew the retaining screws from the solenoid
electrical connection plugs, then pull each plug off of its
respective set of terminals.
NOTE: The plugs are dissimilar and therefore not
interconnectable.
(c)
Remove the four
MS
screws securing the right hand gas
line flange connection to the gas valve.
(d) Remove the screw securing the gas valve support
bracket located within the combustion chamber.
(e)
Release the gas line union connection and carefully
withdraw the valve assembly.
(f)
Unscrew the limit thermostat lead from the rear of the
gas valve.
(g) Remove the inlet elbow and transfer all the ancillary
components to the new gas valve, using seating
compound where necessary.
(h) Re-assemble in the reverse order, taking care to replace
the sealing washer. Ensure that the limit thermostat lead
is correctly positioned in the thermocouple interrupter
before tightening the thermocouple unit.
(i)
Turn on the gas supply at the gas service cock. Refer to
the lighting instructions and light the pilot.
(j)
Check connections for gas soundness.
(k) Turn on the electrical supply. Test for the correct
operation of the gas valve and check for soundness.
1 5.
THE PILOT FILTER
Figs. 1 3 and 24.
Check that the electrical supply and the gas service cock are shut
off.
(a)
Release the cover from the central heating solenoid. There is no
need to remove the electrical connections.
(b) Remove the governor and solenoid assembly by removing the
four pozi·drive screws and put the assembly to one side. Do not
strain the electrical leads. Do not disturb the sealing gasket.
(c)
Remove the single pozi-drive screw securing the exposed
cover plate and carefully lift away the plate.
(d) Replace the pilot filter.
(e)
Reassemble in the reverse order taking great care to ensure
that the gaskets are properly fitted and that the screws are
tight. Replace the gaskets if any damage is apparent.
(f)
Turn on the gas supply.
(g) Turn on the electrical supply. Refer to the lighting instructions
and light the pilot. Check for gas soundness.
(h) Test for the correct operation of the gas valve and check for gas
soundness.
16.
THE SEALED SYSTEM EXPANSION VESSEL
Fig. 25.
(a)
Drain off the central heating and domestic hot water systems.
(b) Remove the gas valve as described in Instruction 14 preceding.
NOTE. Lay the assembly to one side. It is not necessary to dis-
connect the main central heating and domestic hot water
solenoid leads.
(c)
Disconnect the main burner by removing the two extended MS
screws at the combustion chamber. Do not mislay the 0-ring.
(d) Remove the four MS screws and remove the gas line from the
boiler.
21
(e)
Remove the piezo generator as described in Instruction
1 0
preceding. The piezo generator bracket must be removed by
releasing the two MS screws securing it to the vertical
member.
(f)
Undo the union connection joining the expansion vessel to the
heat bank.
NOTE. There will be a small quantity of water remaining in the
heat bank.
Fig. 23.
DHW High Limit Thermostat Reset Button
Fig. 24.
Inlet gas
union cock
111111'111111'11'
Ga(,lve
I
Pressure adjuster
Inner casing fixing screw (6 off).
Overheat thermostat leads
···························~·
\
The~ocouple
Boiler pressure
test point.
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