When it tries to ignite, is the fan running?
As far as I can tell before the boiler ignites of its own volition the fan is not running.
ok, if the fan is not running then it is not an external control fault
It may be a problem with the air pressure switch, if the wind blows into the boiler and it is a bit sensitive
but it would need checking
Would the air pressure switch be in the flue or boiler?
top of the boiler, next to the fan usually
Can you explain you explain the function of the air pressure switch and how it could be causing the problem?
The air pressure switch detects air flown when the fan is running and tell the PCB via a pressure switch that it is running and proceed to the next stage of the ignition sequence.
If the small gasket inside the air pressure switch is stretched slightly then the fan may not produce enough air pressure to keep the APS open all the time, this would make the flame drop out and go back through the ignition sequence, but the fan would be running constantly
I have checked plastic tubes that are attached to the APS and these looked to be alright, but the tube that vents atmospheric pressure from the fan may have been partially blocked, so I replaced the tube. The problem is till evident and te fan defintinety is on when alaced this tube.
I have checked the plastic tubing from the boiler to the APS and these all look to be alright. However, the tube that is connectes the boiler tp atmospherereappearwed t obe partially blokred s I have repalced this tube.d t he fan and spheris
Sorry about the second paragraph but meant to say that I am now looking to replace the APS.
I think that would be the best thing to try first if the fan is running