alpha 240e fan or vac switch

[blocky]

Hi guys. its been a while since i've had boiler problems so cant complain.
Anyway the problem is this.
Came home to discover the ch running but no heat. The fan light was on and the burner would not light. This is the same on both ch and dhw. Took the burner cover off and replaced the silicone pipes from the air pressure switch and switched on ch. It started with no problem but went out as soon as i replaced the burner cover. This was the same with the dhw also. Therefore i'm thinking it's either a lazy air pressure switch or the fan.
Any thoughts?
Thanks.
Ian

 

[twgas]

You need a RGI as this sounds like a gas/flue problem and you are unlikely to get any more advise for that on here.