Boiler makes noise when flame alight. Cuts out after 20s.

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Hi there,

I have a Potterton Performa 24 combi boiler. I have recently drained the system to replace my automatic air vent and to fix a leaking joint (where my CH flow pipe leaves my boiler).

Having just refilled the system and bled the rads, I notice now that the boiler flame only remains alight for about twenty or thirty seconds. About half-way through this time, a whooshing noise slowly grows, peaks (loudly) and dies. The overall effect is similar to a aeroplane flying overhead.

Once the noise has passed, the flame tends to die. The boiler then trundles along without a flame for a minute or two before the process repeats. There are no nasty noises when the flame isn't alight.

My radiators only reach luke-warmth as a result. I feel like something is causing my system to terminate the flame cycle early.

Does anyone have any ideas?

Thanks in advance,

Duncan
 
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have you opened the new AAV?. sounds like it's not properly bled
 
Thanks for the ideas.

The reason I replaced the AAV is because I originally thought the noise was air in the boiler.* Since installation, the new AAV has always had its cap loosened (quite a bit). On a couple of occasions, early on, I heard it vent some air, so I think that bit is working ok.

New bit of info: I discovered this morning that the bad noises only occur when the boiler is heating the CH system. The boiler can successfully heat the DHW system with no dodgy noises.

Perhaps that can help narrow down a subset of components that are only relevant to the CH system?


* I also wanted to replace it because the old one had begun to leak.
 
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if your DHW is working fully the boiler is doing most things it should do. are the CH flow and return valves fully open?
are these problems related to your earlier thread?
 
if your DHW is working fully the boiler is doing most things it should do. are the CH flow and return valves fully open?
are these problems related to your earlier thread?

Thanks for your response. I haven't touched these valves, so I'm assuming they are still open.

These problems are not related to my earlier thread, other than being about the same system. The noises mentioned in my previous thread appeared to just be trapped air, and reduced slowly over time with regular bleeding from my old, leaking AAV.

This afternoon, I had a family friend drop by to inspect the system. He's not a boiler repair expert, but he's a plumbing and heating engineer. He couldn't identify a definitive problem, but he measured and inspected a few things.

Apparently my gas pressure levels are fine. He thinks the CH is cutting out because it was overheating. This seems to match the symptoms (i.e. short burn time and 2-3 minute "cool off" time). The return pipe was stone cold but the flow pipe was heating up fine.

Sadly he couldn't conclude what was wrong and plans to phone the supplier (Potterton) on Monday for ideas.

It seemed to me that the answer lies in whatever parts of the system are not common to both the CH and DHW system. The DHW system can run and run without the flame being aborted or funny noises occurring.

Any thoughts on what could cause only the CH part of the system to overheat?

Thanks,

Duncan
 
well, if the DHW is good then overheating would seem to be the problem. can you visibly check to see that the valves are fully open?
normally from cold HW starts to circulate but usually the flow is only warm to start with, gradually getting hotter as the whole system warms up. i'd be looking to find out why the circulation is reduced enough to make the water hot enough to go to overheat
 
Perhaps draining down has disturbed debris in the sysstem...have you thought of checking the filter located in the front of the return isolating valve?
 
Good ideas. I'll try to investigate the filters (and double check the valves).

Some kind of blockage seems like a sensible diagnosis to me, especially considering the DHW is fine.

Thanks. I'll let you know how it goes.
 
have you thought of checking the filter located in the front of the return isolating valve?

The system has been running for five minutes now without problems. There was some debris in the filter and clearing that has certainly improved the situation. Fingers crossed, maybe it's fixed! Thank you very much for the advice.

Incidentally, my filter is fitted onto my flow pipe, not my return. Is this wrong? It seems to me it should be on the return (as you suggested), to prevent debris making its way into the boiler.

Thanks in advance,

Duncan
 
Apologies for the bump, but I'd really appreciate someone's quick advice on this question as I'd like to drain the system (for the final time) tonight.

To recap:

My CH return pipe has no filter; instead my CH flow pipe has a filter. This seems wrong to me. Surely debris should be captured prior to entering the boiler.

As the fittings are of the same system, would anyone support my idea of moving the filter to my return pipe?
 

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