Humming radiator noise

[asalcedo]

I have installed two new Worcester 30 CDi System boilers at home.

All is well except the noise that comes from the radiators when the pump is working.

It is a humming noise. Like a murmur. It is the sound of the water flowing through the radiator or valves.

In the quiteness of the night it can be quite disturbing. Enough to wake people up.

With the older Vokera boilers that I had before, this noise was not perceptible.

In addition to changing the boilers, I gave a good power flush to the central heating system and put inhibitor.

Is this noise due to a higher water flow speed with these newer boilers?

Is there a way to reduce the noise without compromising the system efficiency much?

Thanks,

Antonio

[RW]

Change the flow rate and see if it disappears

[tonyjeffs]

We had the same problem immediately after new ch installed, but it went away after a week. I figured it was bits of trapped air that needed time to sort themselves out. Same might happen for you.

If not, is it near the boiler, or in the radiator loops? You could try isolating parts of the system by fitting isolator valves and see if you can localise it.

[The Natural Philosopher]

You will get this on any system. There is always some outgassing from the pipes. In practice the bubbles get carried to a local high point - one rad always has a cold top. Bleed that, re-pressurise if needs be, and robert is a relative.

[asalcedo]

This problem is becoming now a big issue.

More information:

If I close the valves in any radiator, it disappears in that radiator.

The radiators have been bled fully several times.

I do not think there is any trapped air in the system because a power flushing pump was used to do the power flush and since then no air has been let inside. The power flush pump would have easily removed any trapped air.

System does not lose any pressure and no new water has been fed in.

I believe the noise is similar to the noise that the boilers make when the pump is working. It is just amplified in the radiators.

The boilers are working fine, they are brand new and have been inspected by the installers and by two Bosch engineers recently for an unrelated issue.

The bigger the radiator, the bigger the noise.

It happens with all radiators in all four zones of the central heating system. The system has a total of 25 radiators.

The main inconvenience is in the top floor, where the bedrooms are.

There are four radiators on that floor. When all four of them are working the noise is lower. When only one or two are working, the noise is louder.

I have contacted Worcester tech support and they say that the pump speed cannot be altered. They only suggest that I bring in one of their engineers for a chargeable call but give little hope that the problem can be solved.

Any more ideas?

Thanks,

Antonio

[Bruce]

Could it be a form of water hammer?

[asalcedo]

No, it does not seem to be water hammer at all. Water hammer, according to Wikipedia, is a pressure surge or wave resulting when a fluid in motion is forced to stop or change direction suddenly (momentum change). Water hammer commonly occurs when a valve is closed suddenly at an end of a pipeline system, and a pressure wave propagates in the pipe.

In my case there is no valve being closed. In fact, when the radiator valve is closed all noise ends.

I have put my ear against the boiler while the pump is working and I can hear the same noise. There seems to be also a fan working at the same time as the pump is.

I strongly believe now that the noise at the radiators is the pump/fan noise.

It seems that these new boilers work with a higher pump speed which leads to higher water flow.

According to Worcester tech support there is no way to lower the pump speed in my boilers (which are supposed to be good quality and expensive ones).

I am willing to change the boilers.

Are there other good quality boilers that will not give me the same problem. Perhaps by allowing a reduced pump speed when needed?

Would a plate heat exchanger, with the same boilers solve this problem?

If so, what does it entail to have a plate heat exchanger installed?

Thanks,

Antonio

[Rod]

The WB documentation states:

"Variable pump speed* Automatically adjusts to meet system flow demand"

So while the pump speed may not be manually adjusted, it is supposed to adjust itself automatically.

Therefore I suggest you try adjusting the temperature control upwards - higher temperature should reduce the systems' pumping requirements - hence reducing pump speed. At least that is how it appears to me.

Of course, this might mean the boiles do not condense so effectively and will run less efficiently. But compared with the cost of replacing them, this would almost certainly be marginal.

If anyone wishes to add/subtract from this feel welcome - I am no expert.