38
Does the fan run
before the fault
occurs?
Turn off boiler. Is there
continuity across the
C
and
NO
terminals of
the air pressure switch
(where green wires are
fitted)?
Remove the fan
connector from board
position
ST1
and
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
.
Repair or replace fan
(Section 15.4.13) or
cable.
Air pressure switch
is shorting.
Replace switch.
(Section 15.4.22)
Replace control board.
(Section 15.4.10).
FAIL POINT J “Air Pr
essur
e F
ault”
No
No
No
Yes
Yes
Yes
Does the burner ignite
(burner light on)
before fault occurs?
Pressure switch has
opened during
operation.
Check flue for
blockage.
Also investigate sense
tubes and pressure
switch.
Remove electrical
connectors from
pressure switch and
restart boiler. Is there
continuity between
C
and
NO
terminal
(where green wires
were fitted) when the
fan runs?
Pressure switch has
not closed. Are the
silicon tubes in good
condition and free of
condensation.
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.
Inspect the flue. Is it
free of any
restrictions?
Rectify flue problem.
Remove multiway
connector from board
position
ST16
. Is there
continuity of the
green wires?
Replace control board.
(Section (15.4.10).
Repair wires or replace
harness.
Replace tubes. If
condensation has
occurred, also replace
pressure switch and
check condition of
Venturi in the fan.
No
No
No
No
No
Yes
Yes
Yes
Yes
Yes