28cdi weird fault.

[Millsy 82]

So I went out for a service a week ago and they said it stops working and the hot water light flashes (air pressure fault).

I wasn't 100% certain what it was I narrowed it down to the fan slowing down for a split second when it gets hot or the aps drops out for a second and it cuts out. Because it didn't happen all the time it was difficult to pin point it.

What I did was
Checked aps hoses.
Power to fan ok.
Full strip down with analyser at end all fine, bp fine and gas rate fine.

So went back with fan and aps. Turns out it was neither.

They said it can only be fan or aps but to check flue as it might not be getting enough air. I did say if it wasn't getting enough air then co would be high.

It is impossible to check the flue completely as I would need scaffolding as the flue is coming out of the wall above the garage roof so can't get a ladder to it and can't reach off the roof.

I have looked down the flue from the test point and all looks ok. I've had the fan out and double checked the hood etc for cracks. Flame picture is spot on (I had to sit and watch for about 20 minutes before it locked out.)

So any other ideas?

 

[ed209]

Could be partly blocked primary heat exchanger, I had a GW micron Heat only the other day similar symptoms to yours connected my power flusher to F&R ( drain down system, cut pipes to connect to boiler only) put some system cleaner in left it running alternating flow now and again, went off had lunch left power flush running, reconnected to system, boiler running like new no cutting out/ lock out

 

[Gas74]

Check to see if there is a restrictor ring in flue if so remove and test had a good few with this issue and this seems to resolve. And it does not affect any combustion readings etc.
Because of this I have often wondered what the point of the restrictor ring is in the first place ?.?

 

[bassmonster]

i've got the same boiler in my house with the exact same problem...i've not had a chance to have a proper look...the rest button always sorts it out....it's completely random...at times, a good couple of weeks will go by without any issues...