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Remove BROWNand
WHITE terminals
from air pressure
switch
Air pressure switch
faulty
With no demand, is a
short-circuit observed
at exposed APS
terminals?
Reconnect the
WHITE & BROWN
wire and remove the
GREEN wire. Initiate
a demand.
Does the fan run?
PCB faulty
Air pressure switch
faulty
APS OK
Is gas pressure present
at input to gas valve?
Ensure gas supply
Faulty board
Replace
Faulty gas valve
Replace
Is live output present at
X5 pins 1 & 2 relative to
neutral at pin 3?
Is gas pressure present
at input to burner?
Gas valve OK
With fan running
disconnect BROWN
wire. (DO NOT touch
chassis with it). Is a
short circuit observed
across exposed APS
terminals?
Gas Valve Check
NO
NO
NO
YES
YES
YES
YES
YES
NO
NO
NO
Air Pressure Switch Check
Is there mains 230V
at fan connector X4
pins 1 and 3?
YES
Fan or fan cable
faulty
NO
YES
L