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Remove connector
X5 and test
resistance between
the red and violet
cables. Is the
resistance between
1 kohm and
30 kohm?
FAIL POINT A
No
Yes
NOTE: It is normal to see only a
demand light if the boiler is hot
and the burner has temporarily
shut off.
Ensure boiler is cool and user
control set to maximum.
Replace sensor
or check
cables to it.
Gain access to the
control board.
Is there 230V at connector
X1 between pins SL & N?
Replace control board.
Yes
No boiler demand
from the heating
system. Investigate
system.
No
FAIL POINT B
Gain access to the
control board.
Is there 230V at connector
X1 between pins
'PERM LIVE' & 'N'?
No permanent live
supply to control
board. Investigate
electrical supply from
external system.
No
Create a new demand.
Does the fan run?
Yes
No
Is there 230V
across the fan
terminals?
WARNING:
if NO, both fan
terminals will
be LIVE.
Does the
pump
run?
Check fuse F1
on the control
board.
Has it blown?
No No No
Replace fan.
Yes
Air pressure switch
is stuck on.
Replace air pressure
switch.
Yes
Replace fuse and
investigate cause.
Suggestions:
connections to (or
faults within) pump,
fan, gas valve,
system wiring,
possible board fault.
Yes
Does the fan run
continuously?
Fan cycles on & off.
Is there any sign of
blockage in the flue or
air pressure tubes?
No
Replace control board.
No
Yes
Yes
Clear blockage.
Yes
Air pressure switch not
changing over. Check flue and
air pressure sense tubes. Are
they clear and not damaged?
No
Repair fault.
Replace air pressure switch.
If this does not solve the
problem check the venturi in
the fan housing.
Yes