Boiler Fan Issue?

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Stirlingshire
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Have a Feroli Modena 102 combi which has a concentric vertical flue.

It was cutting out during hot water demand when we bought the house and a boiler guy came round and diagnosed a faulty fan. New one fitted and issue was resolved.

Over time the boiler has started to get quite noisy with lots of sucking sounds. Friend who is a boiler engineer came round and found that the seal around the case had part of it missing so replaced that and the gasket for the flue as the original was misshapen and wasn't sitting right.

Closed it all up and it was running nice and quiet. Great.

Went to run the bath for the kids this evening after the heating had been on for a bit and although the hot was was fine, the boiler started to really bang and rattle. Much less so when it was on but with no hot water demand. I have a video of it but can't post it here. It sounds just as it did when we moved in although it isn't cutting out.

Any ideas why it could be struggling for air (at least that's what it sounds like)?

Cheers.
 
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sounds like vitiation is taking place on the burner assembley , this is s result of combustion products leaving the boiler within the flue outlet duct returning within the air intake duct and reentering the combustion chamber causing a reduced oxygen level for new combustion resulting in the flames lifting off the burner as they search for oxygen to stabilise . this re entry of combustion product takes place when a flue joining bracket within the outlet flue duct corrodes and separates allowing the products of combustion to leak into the surrounding air duct . You will need a gas safe engineer to carry out this repair as a flue analyser will be reqd to check for correct combustion all innaccordance with the manufacturers instructions. hope this helps ( boiler medics )
 
Thanks for the new reply. What's odd is when he had serviced it he did all the relevant tests and there was no unusual reading suggesting there was an issue with the flue. The incoming air was clean.

It was only after it ran for a short time that it began knocking. It now knocks immediately if the case is fully sealed.

Also got a CO detectors in the boiler cupboard and the loft where the flue is and neither have reacted.
 
you won’t get the company detector going off because the leaking combustion products are staying within the air intake duct (white flue pipe ) returning into the boiler , that’s why when the combustion front panel is removed the flames stabilise because they don’t rely on the balanced flue effect of the vertical flue system , plenty oxygen can get directly into the combustion box . if you can see through the sight glass in this combustion panel you may be able to see the flames instability as they lift off the burner causing the vibration within the sealed combustion box . other possibility is that the fan had separated frim the flue outlet connection if it wasn’t secured into the flue seal correctly by gate installer .
 
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It's from the main covered area rather than the pipework or electrics below. It disappears completely when you open the case and if you just crack the case open you can hear and feel the air being sucked in.
 
you will feel the air being drawn in thats normal, you however should not be doing that it can be extremely dangerous you should not be touching that case seal, from your video you do not have flame lift off the flame picture is normal
 
Definately sounds mechanical and if it stops when the combution cover is removed that only leaves the fan, when fitting the fan assembly on these there is a small lug that you lock in to the flue collector, if this hasnt been located properly that might be your problem as the fan will vibrate trying to draw combustion air through the flue but when you open the cover it will just draw the air from the room, we are getting very close to contravening the rules of the site here now though as you shouldnt be opening that cover, you really need a GSR to inspect the fan installation and see if it is located properly , its easy to fit it wrongly
 
I understand the dangers, don't worry. Whenever a non obvious problem comes up I always find that it's worth asking to help get to a quicker solution rather than waste lots of my mates time. Anything other than checking if something is seated correctly I'd get him round.
 
when fitting the fan assembly on these there is a small lug that you lock in to the flue collector

And the points go to Ian! Took the fan out to check the Venturi and noticed the lug at the back was bent over so wasn't sitting correctly on the flue assembly. Straightened it up and ensured it locked in when the fan went back in.

No more noise.

Getting mate to come back out and test the flue gases again.

Thanks for everyone's help.
 
the flames are very unstable due to an imbalanced combustion chamber and from hearing that rattling noise from the videos i have to agree with ian the fan sounds loose on its fixing or the fan mounting lug had sheared off or its impeller is becoming loose on the fan shaft causing a reduction in the air flow through the chamber .
 

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