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Combi system - strange noise

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staffordian
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Combi system - strange noise

#177223

Postby staffordian » October 30th, 2018, 7:29 pm

Over the last few days our combi system has started to make a strange noise and I wondered if anyone might have an idea of it's cause.

The noise sounds like a low pitched trombone or foghorn type sound, which lasts about half a second or so, but is loud enough to hear from most rooms. It happens about a minute or so after running a hot tap. There is no sound whilst the taps are running. It doesn't happen every time, but does more often than not.

The sound is definitely not coming from the boiler, it seems to be coming from the loft, where hot water pipes run from the boiler to the bathroom, but the sound happens when either the hot tap in the kitchen or in the bathroom has been used, and the pipe run to the kitchen tap goes nowhere near where the noise seems to come from.

We had a new boiler fitted a few months ago, though the pipework is much older so I shall call out British Gas, who fitted the new boiler and cover the whole system.

However as it is a bit of an intermittent issue, it would be useful to have an idea of what the issue might be before contacting them.

Thanks for any advice.

Staffordian

Itsallaguess
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Re: Combi system - strange noise

#177229

Postby Itsallaguess » October 30th, 2018, 7:55 pm

staffordian wrote:
Over the last few days our combi system has started to make a strange noise and I wondered if anyone might have an idea of it's cause.

The noise sounds like a low pitched trombone or foghorn type sound, which lasts about half a second or so, but is loud enough to hear from most rooms. It happens about a minute or so after running a hot tap. There is no sound whilst the taps are running. It doesn't happen every time, but does more often than not.

The sound is definitely not coming from the boiler, it seems to be coming from the loft, where hot water pipes run from the boiler to the bathroom, but the sound happens when either the hot tap in the kitchen or in the bathroom has been used, and the pipe run to the kitchen tap goes nowhere near where the noise seems to come from.

We had a new boiler fitted a few months ago, though the pipework is much older so I shall call out British Gas, who fitted the new boiler and cover the whole system.

However as it is a bit of an intermittent issue, it would be useful to have an idea of what the issue might be before contacting them.


Sounds like the ball-valve in a hot-water header-tank, although you've not specifically said if there is one on your system?

When you have one and you run hot water, the valve will open to replenish the tank, and these can become noisy in the way you describe, especially when things start to get a bit parky in the loft.

Have a nip up there and ask someone to run the hot-water tap - you should be able to quickly hear if it's the ball-valve, and you could manually operate it to close it and instantly hear the noise stopping, just to be sure.

Although it might be possible to replace the noisy washer, it's not usually a big job to replace the whole ball-valve. Some relief can sometimes be had by adjusting the ball-valve setting, but it's probably just as well to swap the valve out with a new one.

Also, have a look at local pipe-clipping to see if any could be fixed down better whilst you're up there - poorly clipped pipework can magnify these types of noises a lot of the time.

Whilst you're up there, check for pipe and tank lagging as well - if your loft is well insulated then these spaces can become very cold over a harsh winter, and you won't want pipes freezing....

Cheers,

Itsallaguess

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Re: Combi system - strange noise

#177233

Postby staffordian » October 30th, 2018, 8:15 pm

Hi Itsallaguess,

Thanks very much for your thoughts. I wish it were that simple, but unfortunately there are no tanks or valves up there, just pipe runs. The previous owners had the tanks taken out when it was converted to a combi set up so the hot water is heated on demand from a cold water supply fed straight from the mains to the boiler.

I do plan to get up there to see if I can pin down the location a bit more precisely, though we have a bungalow with a very shallow pitched roof, which means crawling about up there is not high on my list of life's pleasures :)

I do know that the pipes are pretty well protected from freezing though, it was one of the things I checked soon after we moved in.

Staffordian

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Re: Combi system - strange noise

#177234

Postby Itsallaguess » October 30th, 2018, 8:21 pm

staffordian wrote:
I wish it were that simple, but unfortunately there are no tanks or valves up there, just pipe runs. The previous owners had the tanks taken out when it was converted to a combi set up so the hot water is heated on demand from a cold water supply fed straight from the mains to the boiler.

I do plan to get up there to see if I can pin down the location a bit more precisely, though we have a bungalow with a very shallow pitched roof, which means crawling about up there is not high on my list of life's pleasures.

I do know that the pipes are pretty well protected from freezing though, it was one of the things I checked soon after we moved in.


Ah - sounds like an air-trap then, especially given the recent works on the system....

The sound might possibly be enhanced with poor clips too, but not necessarily so.

Cheers,

Itsallaguess

staffordian
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Re: Combi system - strange noise

#177236

Postby staffordian » October 30th, 2018, 8:24 pm

Thanks again, that sounds feasible.

Sounds like a phone call beckons, to get the experts out.

Staffordian

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Re: Combi system - strange noise

#177692

Postby stewamax » November 1st, 2018, 9:41 pm

Since it is a combi, it could be the effect on the CH circuit (not HW piping) as the diverter valve in the combi switches back from 'HW priority' to 'CH priority and the CH system then has a sudden flush of hot water. I would be inclined to sit by each radiator in turn and get someone to turn the hot tap on and then off.

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Re: Combi system - strange noise

#177702

Postby staffordian » November 1st, 2018, 11:10 pm

stewamax wrote:Since it is a combi, it could be the effect on the CH circuit (not HW piping) as the diverter valve in the combi switches back from 'HW priority' to 'CH priority and the CH system then has a sudden flush of hot water. I would be inclined to sit by each radiator in turn and get someone to turn the hot tap on and then off.


Thanks stewamax. We have tried pinning the noise down and though it is audible from all rooms, the source appears to be the loft rather than a radiator. We have an engineer coming on Monday, so fingers crossed, the issue will be resolved.

I'll report back here, just in case it helps someone else in the future.

Staffordian

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Re: Combi system - strange noise

#177710

Postby Dod101 » November 2nd, 2018, 2:37 am

When it comes to questions like this, I often wonder if I am particularly fortunate to live in a rural environment where I know the proprietor of the business and quite probably the operative (the guy who actually does the work) I then simply call him and get him to fix it. The big national firms like Centrica are fine unless something goes wrong.

Dod

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Re: Combi system - strange noise

#178241

Postby staffordian » November 5th, 2018, 2:12 pm

The problem is now resolved. It stemmed from a radiator in our hall on which I had almost closed the lockshield valve because the rad was getting too hot. When the boiler shut off (or switched to heating) after supplying hot water, it must, as stewamax suggested, have sent a pulse of water through the CH pipework, and I guess this rad was the first it came to, and the almost closed lockshield valve created an obstruction. Opening it a little, and closing down the valve at the other end instead seems to have solved it, The reason the sound was hard to pin down was that the pipework involved was boxed in where it dropped from the loft down to floor level, and it seems the sound travelled up the boxing-in towards the loft.

The problem now is ensuring no-one is tempted to open up this valve. The programmable thermostat is in the hall, and the hall has internal walls only, so retains it's heat. Therefore if the rad is turned up and gets as hot as the others then the hall heats up quickly, the heating goes off and stays off for ages, not allowing the other rooms to get warm enough. I guess an answer is a wireless stat we can move into the lounge but I'd rather stick with the current setup if possible. Time will tell...

Anyway, many thanks to all for the suggestions and advice.

Staffordian

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Re: Combi system - strange noise

#178460

Postby stewamax » November 6th, 2018, 11:07 am

It is also worth a simple check that the radiator concerned hasn't been plumbed in backwards.
OP didn't mention whether or not it was fitted with a TRV, but it's worth remembering that older TRVs may be one way (they will have an arrow on the valve case). New ones such as the ubiquitous Dratyton TRV4 are (in theory) bidirectional, although are usually fitted on the flow (hotter) end with the lockshield valve on the return end. I know from personal experience that their predecessor TRV3s were, in practice, not bi-directional, and would thump and whine when the flow changed (e.e. when the pump started).

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Re: Combi system - strange noise

#178475

Postby pochisoldi » November 6th, 2018, 11:32 am

staffordian wrote:The problem is now resolved. It stemmed from a radiator in our hall on which I had almost closed the lockshield valve because the rad was getting too hot. When the boiler shut off (or switched to heating) after supplying hot water, it must, as stewamax suggested, have sent a pulse of water through the CH pipework, and I guess this rad was the first it came to, and the almost closed lockshield valve created an obstruction. Opening it a little, and closing down the valve at the other end instead seems to have solved it, The reason the sound was hard to pin down was that the pipework involved was boxed in where it dropped from the loft down to floor level, and it seems the sound travelled up the boxing-in towards the loft.

The problem now is ensuring no-one is tempted to open up this valve. The programmable thermostat is in the hall, and the hall has internal walls only, so retains it's heat. Therefore if the rad is turned up and gets as hot as the others then the hall heats up quickly, the heating goes off and stays off for ages, not allowing the other rooms to get warm enough. I guess an answer is a wireless stat we can move into the lounge but I'd rather stick with the current setup if possible. Time will tell...

Anyway, many thanks to all for the suggestions and advice.

Staffordian


Why not leave the TRV open full (or even remove the sensing head entirely), and then use the lockshield valve to reduce the heat output from the radiator.

That way you close the control loop, with the room stat turning the boiler off when the last room (and the whole house) has reached temperature.

If you turn the hall radiator off, then you are either relying on escaping heat from other rooms to tell the room stat to turn the boiler off, or the system will end up cycling on the boiler stat, in both cases running the boiler when the real demand for heat has been satisfied.

PochiSoldi

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Re: Combi system - strange noise

#178486

Postby staffordian » November 6th, 2018, 12:03 pm

To answer the two above posts, the hall rad does not have a TRV, presumably because it is the room in which the room stat is fitted.

Until last year this room stat was the ubiquitous Honeywell dial stat; as much use as a chocolate fireguard, so we more or less controlled the system with the timer by the boiler.

Last November, after recommendations here, I swapped the Honeywell stat for a Salus programmable stat and found it to be a well worthwhile upgrade, the only slight issue being that I had to ensure the hall rad didn't get too hot for the reasons mentioned earlier.

So to answer pochisoldi's suggestion above, it was adjusting via the lockshield valve which unwittingly led to the noise problem in the OP.

Adjusting the rad via the adjustable (nonTRV) valve seems to be doing the trick, so hopefully all is now good.


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