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Carry out preliminary electrical checks to
make sure the electrical supply is available
at the boiler. Check that external controls
are calling for heat. Make sure that the
system is filled, the flue blockage safety
device is reset, the gas supply is available
and the pilot is lit.
Isolate electrical supply to the
control box.
Remove the control box cover and
check all cables.
Turn boiler thermostat to Max.
Is there continuity between
'C' and 'NC'.
Turn boiler thermostat to 'O'.
Is there open circuit between 'C'
and 'NC'.
Restore electrical supply with pilot
burner lit and boiler thermostat set
between 'MIN' and 'MAX', does the
main burner light.
Turn boiler thermostat to "O'.
Does main burner extinguish.
Boiler controls in order.
FAULT FINDING
Supplied By www.heating spares.co Tel. 0161 620 6677
9 Fault Finding
YES
YES
YES
YES
19
NO
Faulty thermostat.
Replace.
NO
NO
Faulty gas valve.
Replace.
NO
Diagram 9.4
221787B
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