Intermittent Air Flow Fault

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Hello all, first post here so be gentle with me!

I am the (not so) proud owner of an archaic WORCESTER 28CDI combi.

Around Xmas time the boiler made some horrible loud grinding noises and then gave up completely, RGI came round and diagnosed the fan.

Brand new fan fitted and then the boiler immediately started displaying an air flow fault when attempting to use either the HW or CH - it had never shown this fault before. It then seemed to start working ok again that evening.

The following day the air flow fault continued whenever we attempted to use HW or CH, after several power on/off resets it would work.

The original RGI was unavailable so I called out another company after getting it in the lughole from the wife, they checked the fan/venturi was clear - it was, I checked the flue from outside as best I could and it was clear too, they checked the gas valve and set this up according to Worcester specs. This RGI said the APS sounded like it wasn’t working correctly and was chattering so a new APS was ordered and fitted - when he left the boiler was warmed up and working. An hour later the intermittent air flow fault started again.

I got told it might be the PCB and so a refurbished PCB was ordered and fitted, same fault continues!

The boiler seems to work ok once it’s warmed up. It’s not losing pressure and when it is working all rads and water are red hot.

I’m stuck on ideas and fast losing patience and money trying to solve the mystery - if anyone has any ideas it’d be much appreciated, otherwise I’m just going to have to buy a new boiler

Cheers
Gary
 
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Cant go into too much detail as most things to check are in the combustion chamber. The fault finding process has been described pretty much as i would have hone through it. I suspect the fault may lie in the original fitting of the fan but hard to be sure. May be time to cut your losses and fit a new boiler or get someone who really knows this boiler.
 
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We had this similar problem, first the PCB was replaced to fix a fault, then the new one would light then cut out with a pressure switch problem, aps was replaced, then it turned out the aps was already not piped correctly, one end was actually on the flue test point opening which was left open and the other was in the Venturi where it should be.
The correct piping didn't help, then we realised the fan pressure flow was registering low. Long story short the flue when the flat was built was fitted about 50% longer than allowed in all the flats with that layout. Changing the PCB had made it more sensitive, and it was a case of replacing the whole boiler (and fitting ugly hatches all over the lounge ceiling, glad it was a rental...)

The repair guy didn't have a clue, nor did i, he tried everything, the landlord thought he was trying to rip her off!
 
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Thank you for the replies. I’m pretty confident it isn’t the flue that’s the issue. I’m getting an RGI to replace all of the tubing from the fan down to the APS and see if that resolves the issue.

If not I read another thread where the flame rectifier and/or spark electrodes and harnesses can cause the same fault - so that’ll be the last thing to replace as it’s cheap.

If none of the above works then I’ll be getting a new boiler I reckon!
 
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Cant go into too much detail as most things to check are in the combustion chamber. The fault finding process has been described pretty much as i would have hone through it. I suspect the fault may lie in the original fitting of the fan but hard to be sure. May be time to cut your losses and fit a new boiler or get someone who really knows this boiler.

Yeah I thought it might have been the fan fitment but the second RGI I had come out removed the new fan and then refitted it to make sure it was all correct.
 
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