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Before tests ensure
pump has stopped
NO
Set the operating switch
(or programmer)
to HEATING and WATER
and turn the heating
control stat and room
thermostat (if fitted) to
maximum (but keep the
hot water control stat
in the OFF position).
Does the DEMAND
lamp illuminate?
YES
NO
Does the pump run?
YES
NO
Does the fan run and an
automatic ignition
sequence occur,
ending in full
burner ignition?
YES
NO
Does the burner operate
at or near minimum
gas pressure?
YES
NO
Does the diverter
valve operate?
NOTE: This failure
would cause cold
water at the flow
outlet and the boiler
will cycle on the
heating control stat
YES
END OF
CENTRAL HEATING
TEST
START OF CENTRAL HEATING TEST
NO
Is there 230V at
pin 4 of
terminal X12?
(C.H.)
YES
NO
Is there 230V at
pin 2 of
terminal X13?
(Right roomstat
terminal)
YES
Is there approx. 90V
NO
at pin 5 of terminal
X3? (DEM).
Note: Lamp is not
supplied directly by
mains voltage
YES
Replace demand
indicator
Replace the
control board
NO
Is there 230V at pin 3
of terminal X15?
(Right white wire)
YES
Replace the
control board
Replace the
gas valve
NO
Is there 230V at
pin 3 of
terminal X7?
(Brown wire)
YES
Replace the
diverter valve
54
Replace the
operating switch
(or programmer)
NO
Is there 230V at
pin 3 of
terminal X13?
(Left roomstat
terminal)
YES
Replace room thermostat
or insert optional link
Replace the
control board
NO
Is there 230V at pin 2
of terminal X15?
(Left white wire)
YES
Replace the
heating control stat.
Replace the
control board
Replace the
control board
Replace the
control board
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