Boiler Noise driving me nuts

[Eternal Heating]

I had a new boiler fitted last January 2015. My previous boiler worked well, but 10 years later I decided an upgrade was necessary.

A short time later, I got the rumbling noise. It was as if there was a Bus or truck parked outside the house, more so only in one room. However, when this does start to happen, the boiler also gets notably noisier.

After the pump was replaced it looked like it had been fixed, but the noise returned. Through lots of different attempts to isolate the problem, it became apparent that simply draining the boiler & refilling it has the effect of curing the problem, but again after several days it returns or even sooner in the winter when the boiler is on for longer periods.

I have also noticed that when the noise is apparent, if somebody calls for water, the noise lessens.

One year later, the manufacturers scratching its head, and the easy way out, is to conclude that the problem is with my system, but only since the new boiler when in, and only after a few days of use.

logic says that because the system has been there 10 years (and its clean), and the issue is not apparent when the boiler is drained and refilled, it has to be something that is happening and building in the boiler when it is used.

I thought I’d start positing this, in the hope that somebody might shine some light on this annoying fault.

 

[muggles]

Please provide some useful details...the make and model of the boiler would be a good start!

 

[bernardgreen]

Does this new boiler have a significantly higher heat output rating than the previous one.

One possibility is that the boiler's rated heat output is too large for the system and therefore the boiler is reducing the amount of heat it is producing by reducing the amount of gas and air fed into the combustion chamber. Fan speed is often reduced as part of this reduction and therefore there is less pressure to push the combustion products out of the flue. This reduction in pressure can result in turbulence in flue and even sometimes in the combustion chamber. Turbulance creates noise.

Calling for hot water requires the boiler to increase heat output. Faster fan, more pressure, less likelyhood of turbulance.

Compare the size and speed of the exhaust plume when the boiler is noisy and then when it is running quietly.

 

[Eternal Heating]

Does this new boiler have a significantly higher heat output rating than the previous one.

One possibility is that the boiler's rated heat output is too large for the system and therefore the boiler is reducing the amount of heat it is producing by reducing the amount of gas and air fed into the combustion chamber. Fan speed is often reduced as part of this reduction and therefore there is less pressure to push the combustion products out of the flue. This reduction in pressure can result in turbulence in flue and even sometimes in the combustion chamber. Turbulance creates noise.

Calling for hot water requires the boiler to increase heat output. Faster fan, more pressure, less likelyhood of turbulance.

Compare the size and speed of the exhaust plume when the boiler is noisy and then when it is running quietly.

It is bigger,

My old boiler was a 32kw and this is a 40Kw boiler.

I thought this was only applicable to the hot water side.? If I reduce the temperature for the heating side, would that help?

I asked about the speed on the pump, but I was told todays pumps are self-regulating

 

[bernardgreen]

I thought this was only applicable to the hot water side.? If I reduce the temperature for the heating side, would that help?

This is the dis-advantage of combi boilers. The heat output required to provide a good flow of hot water on demand is much higher than the heat output required to keep the house warm.

Hence the boiler has to be able to work in three different modes

1. high output for heating hot water on demand
2. low output for heating the house
3. high output when heating house and hot water is demanded.

Designing a single chamber combustion system that is acceptably efficient at both high and low heat outputs is not an easy task given the constraints of size and cost that apply in the domestic boiler market.

Reducing the temperature on the heating side is un-likely to help if it reduces the heat output required when heating the house and no demand for hot water.

 

[Eternal Heating]

This is the dis-advantage of combi boilers. The heat output required to provide a good flow of hot water on demand is much higher than the heat output required to keep the house warm.

Hence the boiler has to be able to work in three different modes

1. high output for heating hot water on demand
2. low output for heating the house
3. high output when heating house and hot water is demanded.

Designing a single chamber combustion system that is acceptably efficient at both high and low heat outputs is not an easy task given the constraints of size and cost that apply in the domestic boiler market.

Reducing the temperature on the heating side is un-likely to help if it reduces the heat output required when heating the house and no demand for hot water.

Does this mean, that the only way to sort this would be either to put a lower output boiler in, or put lots more radiators in to dissipate the heat.


Also if the above is true, then why would the noise go away if you drain down and refill the boiler, and why does it only occur after the boiler has been running for a week or two and not immediately. What do you think is building up inside the boiler that eventually causees the noise.

 

[Eternal Heating]

Does anybody have any other theories on my issue?

 

[Razor900]

Please provide some useful details...the make and model of the boiler would be a good start!

Do you mean to say that you can't diagnose it from the vast array of information we've been supplied with? Just because it could be any make, model or type of system. We can sort of guess that it's a combi and it's most probably white!!

Sounds more like a TRV anyway to me especially combined with a 7m pump

 

[ScottishGasMan]

See the room the rumbling is coming from when it happens. The radiator in that room will likely have a thermostatic radiator valve, when you hear the noise turn the valve down as if to turn the heat off to that radiator. Does the noise stop?

Oh and incase your really struggling with reading the above posts, What Make and Model of boiler do you have?

 

[Dan Robinson]

Does anybody have any other theories on my issue?

 

[shambolic]

 

[Razor900]

I'm just bricking it because we do a 40kW combi and I might get the call

 

[simond]

This a good post.

We've got an OP who is determined not to tell us what boiler he's got; and Bernard has redesigned the humble combi boiler.

Two in one, doesn't get any better?

 

[DeadBeat]

I had a wierd noise from my boiler after removing a radiator, but turned out to be air trapped in the system, after bleeding the rads properly the noise at the boiler went away. have you bled the rads again since? as you should probably do it a few times after the system has been drained as air moves around the system.

 

[Razor900]

I wonder why the OP hasn't posted back on this thread??