Worcester 24SiII Installation And Servicing Instructions page 40

Yes
Replace multiway
connector to position
ST16 (but not fan
connector at ST1) and
reset/restart the
No
boiler.
Is there mains 230V
across the right (L)
and left (N) tracks at
board position ST1?
NOTE: Take care not to
short L to N.
Yes
Replace fan connector
No
ST1.
Remove electrical
connectors from air
pressure switch and
reset/restart boiler.
Is there continuity
between C and NO
terminals (where wires
were fitted) when the
fan runs?
(Test within 30
seconds).
Yes
Does the burner ignite
No
(burner light on) and
run for a short priod
before the fault
occurs?
Yes
Pressure switch has
opened during
operation.
Check flue for
blockage.
Also investigate sense
tubes and pressure
switch.
The gas valve mode
switch (concealed by
the facia side panel)
is not set correctly
Replace control board.
In the unlikely event
of this not solving the
problem replace code
plug.
Pressure switch has
No
not closed. Are the
silicon tubes in good
condition and free of
condensation.
Yes
No
Inspect the flue. Is it
free of any
restrictions?
Yes
Replace air pressure
switch.
Note: In the unlikely
event of this not
solving the problem
inspect the pressure
pick-up (Venturi) in the
fan or fan may not be
running freely.
Remove multiway
connector from board
No
position ST16.
Is there continuity of
black & blue cables to
the air pressure
switch?
Yes
Replace control board.
Turn to 'NORM'
position
40
Replace tubes. If
condensation has
occurred, also replace
pressure switch and
check condition of
Venturi in the fan.
Rectify flue problem.
Repair cables or
replace main harness.