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By following the flow diagram number 6 “NO FLAME”, the point of failure can be
diagnosed.
POSSIBLE CAUSES
No gas
Faulty gas valve/ solenoid
Faulty spark generator
Faulty ionisation electrode
Faulty P.C.B
Minimum burner / ignition pressure low
Badly fitted flue.
FAULT 1
Air Pressure Switch Failure.
5 seconds - 1 sec - 5 seconds
Prior to the ignition sequence starting the P.C.B. will check to ensure that the contacts in
the air pressure switch are in the open position, this check occurs before the fan runs.
Should the air pressure switch be faulty, i.e. the contacts in the switch have remained
closed after the fan shut down from the last time of running. The boiler will fail safe and
lock –out will take place after 15 seconds of demand taking place.
If the contacts are in the normal stand-by position, i.e. open then the PCB will initiate the
fan. As sufficient air flows through the plastic venturi (located in the fan spigot) a
differential pressure is produced and transferred via the silicon tubes to the air pressure
switch. The contacts in the air pressure switch make, and the ignition sequence
commences.
Failure to detect a differential pressure will result in the fan running for 3 minutes before
lock –out takes place. Investigation as to the cause of the switch not activating is usually
required, as replacing the switch is not usually the cure for the fault.
POSSIBLE CAUSES
Insect contamination of the venturi
Faulty Air Pressure Switch
Faulty or Slow running Fan
Air tubes incorrectly fitted or Loose
Test point cap missing
Blocked or badly fitted Flue
Venturi fitted upside down
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