Bosch Worcester 14/19CBI Installation And Servicing Instructions page 36

Gain access to the
control board.
Is there 230V at connector
X1 between pins SL & N?
Yes
Replace control board.
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.
Gain access to the
control board.
Is there 230V at connector
X1 between pins
'PERM LIVE' & 'N'?
Yes
Create a new demand.
Does the fan run?
Yes
Does the fan run
continuously?
Yes
Air pressure switch not
changing over. Check flue and
air pressure sense tubes. Are
they clear and not damaged?
Yes
Replace air pressure switch.
If this does not solve the
problem check the venturi in
the fan housing.
No boiler demand
No
from the heating
system. Investigate
system.
No permanent live
No
supply to control
board. Investigate
electrical supply from
external system.
Is there 230V
across the fan
No No
terminals?
WARNING:
if NO, both fan
terminals will
be LIVE.
Yes
Replace fan.
Fan cycles on & off.
No
Is there any sign of
blockage in the flue or
air pressure tubes?
Yes
Clear blockage.
No
Repair fault.
36
Check fuse F1
No
Does the
on the control
pump
run?
Has it blown?
Yes
Replace fuse and
Air pressure switch
investigate cause.
is stuck on.
Suggestions:
Replace air pressure
connections to (or
switch.
faults within) pump,
fan, gas valve,
system wiring,
possible board fault.
No
Replace control board.
Replace sensor
or check
cables to it.
Remove connector
X5 and test
resistance between
No
the red and violet
board.
cables. Is the
resistance between
1 kohm and
30 kohm?
Yes
No
Yes