Bosch Worcester 15SBi Installation And Servicing Instructions page 33

No
Does the electrode
spark at the burner?
Yes
No
Does the
fan stop
after a few
seconds?
Yes
Boiler has
LOCKED OUT
Replace control board.
(probably due to
overheating). Is
the boiler fully
water
No
pressurised and
is all air vented.
Yes
Switch off mains
supply and remove
boiler front panel and
combustion chamber
cover. Inspect the
primary (red) sensor.
No
Is it fixed securely to
the pipe?
Yes
Remove Molex
connector at X3. Is
there continuity
across the two orange
No
wires? (ensure black
overheat stat is cool).
No
Remove electrical
connectors from the
pressure switch and
restart the boiler. Is
there continuity
across the two switch
terminals when the
fan runs?
Yes
Replace air pressure
NOTE: In the unlikely
solving the problem.
Inspect the pressure
No
Is there continuity
on the two green
wires?
Yes
(Section 15.4.9)
Rectify fault.
Re-fix sensor to pipe.
Replace overheat
thermostat or
harness to it.
33
No
Pressure switch
Replace tubes.
has not closed.
If condensation has
Are the silicone
occurred also replace
tubes in good
pressure switch and
condition and
check condition of
free of
venturi in the fan.
condensation?
Yes
No
Inspect the flue.
Is it free of
restrictions?
Yes
switch.
event of this not
pick up (venturi)
in the fan.
Repair or replace
harness.
Rectify flue
problem