29
221680G
When demand from T/Sat is
requested, does the pump operate?
Is there 230v at
pump?
Change pump.
Does fan go to high speed?
Does main burner light?
Does signal from
air pressure switch
change over?
Winter Mode Continued.
YES
YES
YES
YES
YES
NO
YES
Change P.C.B.
NO
Is there 24v at
modureg valve?
Change valve.
YES
Change P.C.B.
NO
Is there 230v at
fan terminals?
Change fan.
Change air
pressure switch.
YES
Change P.C.B.
NO
NO
NO
NO
Connect a manometer to gas
valve and check burner pressure.
Adjust central heating burner
pressure potentiometer.
Does the burner pressure increase
and decrease accordingly?
Is there a mV signal at
modureg terminals?
Change P.C.B.
Disconnect connections to central heating thermistor
is there a decrease in electrical resistance accross
the terminals as the temperature increases?
Change thermistor.
Reconnect thermistor turn on hot water tap fully.
Does the central heating pump stop?
Change
flow sensor.
Burner pressure increases to domestic hot water setting.
Adjust domestic hot water burner pressure potentiometer.
Does burner pressure alter accordingly?
Change P.C.B.
Slowly close hot water tap.
Does the Burner pressure modulate
down to keep a constant temperature?
Is there a decrease in
resistance accross the
domestic hot water
thermistor as
temperature rises?
Change thermistor.
YES
YES
YES
YES
YES
NO
NO
Change valve.
YES
NO
NO
NO
NO
NO
Change P.C.B.
YES
Turn off hot water demand. Does pump restart?
Change P.C.B.
Does burner pressurere turn to Central heating setting?
Remove central heating demand.
Does burner go out?
Is there 230v at
main valve?
Change valve
O.K.
Change P.C.B.
YES
YES
YES
YES
NO
Change P.C.B.
NO
NO
NO
13 Fault Finding
Diagram 13.4
7493
BOILER FAULT FINDING
