Worcester 28Si Installation And Servicing Instructions page 38

No
Does the fan run
before the fault
occurs?
Yes
No
Does the burner ignite
(burner light on)
before fault occurs?
Yes
Pressure switch has
opened during
operation.
Check flue for
blockage.
Also investigate sense
tubes and pressure
switch.
Turn off boiler. Is there
continuity across the
No
C and NO terminals of
the air pressure switch
(where green wires are
fitted)?
Yes
Air pressure switch
is shorting.
Replace switch.
(Section 15.4.22)
Remove electrical
No
connectors from
pressure switch and
restart boiler. Is there
continuity between C
and NO terminal
(where green wires
were fitted) when the
fan runs?
Yes
Remove multiway
No
connector from board
position ST16. Is there
continuity of the
green wires?
Yes
Replace control board.
(Section (15.4.10).
38
Remove the fan
connector from board
position ST1 and
No
restart the boiler. Is
there mains 230V
across the centre (L)
and left (N) tracks at
ST1? Note: Take care
not to short L to N.
Yes
Repair or replace fan
(Section 15.4.13) or
cable.
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 (Section
15.4.22). Note: In the
unlikely event of this
not solving the
problem inspect the
pressure pick-up
(Venturi) in the fan.
Repair wires or replace
harness.
Replace control board.
(Section 15.4.10).
Replace tubes. If
condensation has
occurred, also replace
pressure switch and
check condition of
Venturi in the fan.
Rectify flue problem.