Problem with my Ariston Eurocombi A27/MMFI

[alwayscurious]

My Eurocombi A27/MMFI does not light up. Water is demanded, fan runs but burner does not light up, no sparking either. I have recently cahanged a new pcb so no problem there.
I had two gas engineers come round both Corgi/Gas Safe registerd, each spending more than couple of hours each time on two/three occasions but to no avail and they simply gave up and now stoped answering my phone calls.

Please help.
Alwayscurious

 

[kevplumb]

any idea of what has been checked ?

 

[alwayscurious]

any idea of what has been checked ?

Thanks! Kevplumb.

One engineer said it might be the pump (but pump is working fine), the other said it is the fan but fan is now working perfectly. Before the fan he sugested it is the air pressure switch. He did replaced to a second hand air pressure switch but the problem is still there. I think the air pressure switch he brought is not the right one because I noticed its specs are not the same as the original one.
Regards

 

[kevplumb]

sounds like fan or aps related

you need an engineer that knows what he is doing by the sound of it

 

[alwayscurious]

sounds like fan or aps related

you need an engineer that knows what he is doing by the sound of it

But the fan is working fine. All the silicon pipes and venturi device is clear too. I do suspect the air pressure switch though. Ay idea how does the APS works? I mean technically.

Regards