Noise in central heating pipes

[liam2308]

New boiler installed and noticed noise from 2 radiators. On the forum a member suggested one way TRVS on the return. Have now replaced the one way TRVs that were on the returns with 2 way TRVs ( 4 in total )but I am am still getting a hammering noise from 2 radiators/pipework. If I turn of radiators no noise if I turn them on noise can be heard. When the systen is initially heating up there is no noise but as temperature gets to operating temperature noise starts. The noise seems to come when the boiler is actually firing. Then dies down when the boiler cuts of. My pump runs continually - so it cannot be the pump. Sludge is not an issue as system has been drained 2 times in the last few weeks and it is very clean. Noise is not coming directly from radiator but from pipework going to these particular radiators. But from what I have read - it could be coming from anywhere in the system as the sound is obviously travelling. Noise is like a dull hammering sound and it is very regular every 3-4 seconds almost sounds as if system was pulsating. Could the problem be the pipes maybe not secured under floorboards.!! Would be grateful for any advice before I start lifting floorboards. Ps All radiators have TRVs except the hall radiator which is where room stat is located.

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[D_Hailsham]

If I turn off radiators no noise, if I turn them on noise can be heard. When the systen is initially heating up there is no noise but as temperature gets to operating temperature noise starts. The noise seems to come when the boiler is actually firing.

The noise is coming from the TRVs which are bouncing. The thermostatic head is trying to close the TRV, but the water pressure is trying to open it.

The system needs to be properly balanced. See How to balance a CH system

My pump runs continually - so it cannot be the pump.

Are you sure?

 

[liam2308]

If I turn off radiators no noise, if I turn them on noise can be heard. When the systen is initially heating up there is no noise but as temperature gets to operating temperature noise starts. The noise seems to come when the boiler is actually firing.

The noise is coming from the TRVs which are bouncing. The thermostatic head is trying to close the TRV, but the water pressure is trying to open it.

The system needs to be properly balanced. See How to balance a CH system

My pump runs continually - so it cannot be the pump.

Are you sure?

It is a long story but basically my boiler is in the garage and I have four wires running through a Horstmann HXL27 just new to replace Diadem 425. These are buried under drive - to run more cables would require digging up drive. These 4 wires supply boiler/pump/motorised valve/and the electric sockets and lighting in garage.Obviously 2 of the wires are feeding sockets and lights all the time and the other 2 wires are feeding heating these are controlled by HX27. Done 15 years ago. New boiler installed recently. Wiring had pump and boiler on and off at the same time although the boiler cycles the the pump stays on. Grant boiler tech people told me that this would damage heat exchanger very quickly - no pump over run here!. I also installed a Honeywell Room/stat-programmer cm927. The HX27 controls power going to boiler and pump. But I have put the cm927 receiver on the boiler only. I have programmed it to knock boiler of 10 minutes before HX27 knocks of power to pump. Effectively a pipe over run for 10 minutes. I am still studying if I can work round this limitation. Possibly a pipe stat on pump with a lower temperature to keep pump running after boiler has knocked of. But power supply limitation is annoying. I could get over it all by moving programmer into garage and setting up proper wiring. But convenience of programmer in the house would be lost. I will check balancing system because as you mention the problem is the TVRs bouncing.