What's causing this loud noise from my boiler?

[davidc123]

My Worcester cdi 30 conventional boiler makes this very loud noise frequently, sometimes vibrates the house:

https://drive.google.com/file/d/1De7RBrHgAUM25bksHJhIfP0Ue_y9s_5a/view

Not sure what's causing it but I've been able to make it happen by having both heating and hot water on at the same time, then turning the room thermostat down so that just the HW is on.

I had a plumber take a look but they've said there are a few things it could be - burner, gas valve, air entrain components, and suggested it might be better to just replace the boiler than replacing things without being sure what the cause is.

So i'm just wondering if anyone here has a more firm view of what could cause this noise?

Thanks

 

[Madrab]

Sounds like you may have a fan issue .... and a little one wanting fed/attention seeking/changed

You need a GSR in, definitely not a plumber who's guessing, to get the case off and diagnose. Going by the sounds of it, it may be pretty obvious what the problem is.

 

[Harry Bloomfield]

Fan bearings shot.

 

[Gasguru]

Sounds combustion resonance between burner and heat exchanger.
When did it last have a full service? The parts would have been £60 minimum and a few hours for a thorough job.

 

[davidc123]

Sounds combustion resonance between burner and heat exchanger.
When did it last have a full service? The parts would have been £60 minimum and a few hours for a thorough job.

Last week. I asked them to service it and look into the noise but they didn't hear it so asked me to send them a recording instead. When they were here the boiler seemed fine as far as they could tell (and it was a GSR)

Does the fact that it seems to happen when it goes from HW + CH to just HW help support it being the fan or burner / heat exchanger?

 

[Gasguru]

What did they do for the service? Parts price, labour price etc.
You mean if HW & CH are on (and there's a demand for both) and you switch the heating off the noise starts?

 

[davidc123]

You mean if HW & CH are on (and there's a demand for both) and you switch the heating off the noise starts?

That's right - there is demand for both then i turn the room thermostat down so CH goes off. If just CH is on and i turn it off then i don't get the noise.

Not sure what they did for the service - it was just an annual boiler service and i left them to it. They mentioned all the stats it's giving look good.

 

[Gasguru]

It only appears to make the noise on HW?
How old is the boiler and has it ever had a full service (needed ever 5 years say)?

 

[davidc123]

HW can be on on its own without any noises. It's only when CH and HW are on then CH goes off. Haven't tried CH and HW on and HW going off.

I moved into the house earlier this year but it looks like the boiler is 11 years old, and it has been serviced regularly, but not sure if they were full services

 

[Gasguru]

Some "services" especially by the insurance lot are known as a "poke & go". Stick the flue gas analyser probe in, print the numbers and job done. No servicing done whatsoever.
Unless there's evidence to the contrary I normally insist on a full service when taking on a new customer....modern boilers can happily cook themselves with old burner/heat exchanger gaskets etc.
Tricky to solve over a forum..I guess the noise could be down to reduced flowrate with just the HW on...maybe pump too high, bypass valve trouble.
A 30kW boiler is pretty big...6 bedder house?

 

[davidc123]

Thanks for the help. They suggested faulty gas valve is most likely but I'm going to get in touch with the manufacturer, see what they think. It's a 4 bed house. Planning some major work next year which will need the boiler to be moved so will probably replace it then, so I'm hoping I won't have have to do that now then move it later.

 

[Gasguru]

No reason not to get 20 years out of that boiler...the heat exchanger design hasn't really changed from 20 years ago and there's many 2003 combi models around.