Hi, I was thinking the same as Martin. All the radiators need to be balanced, so the same amount of water is flowing through them at the same temperature, which is done on the exit valve of the radiators, all the input valves should be fully open, get the system up to heat, and then measure the temperature of each radiator, and close down the exit valve on the hottest one first, and the next one and so on. You need to turn each one down a little at a time and allow the system to settle down every time you alter one. It can be a bit of a long winded job. though.

Regards Nick.

Have you bled the air out of your pipework in your loft? I have automatic bleed valves in my loft.

It sounds like you may have an airlock (not necessarily cured by bleeding). A central heating plumber was unable to get my mother’s to radiators work at all. As I remember, to get the air out I set the pump to full power and closed all radiators except one.

I don’t think it’ll be air, and isolation won’t help – I get the same noise from my towel rail when the system starts up as the pump initially runs at full speed then slows down, at which point the noise disappears (it’s intentionally set up like that).

It’s due to a lot of water tryng to get through a small (and not very flow-friendly) opening either at the lockshield valve or (more unlikely) the adjustable/thermostatic valve on one or more of the rads. Balancing and reducing pump speed should sort it out.

Given time, the water flow will erode the sharp edges inside the valves and reduce the problem, but that’s not really a practical solution. 🙂

Edit – you did deburr all the internal ends of the pipes when fitting as sharp edges there could cause the same sound?

Rob

We had a similar problem when one of the service engineers turned our Grundfos pump up to the full power setting during a routine service. The noise in the house was unbearable and once I had returned it to the auto setting all was fine.

From what you say I reckon your pump is working flat out to get sufficient water flow. While a larger pump may be working well within its capacity the required quantity of water circulating might well give the same problem.

I would consider two pumps running in tandem. One for the underfloor heating and one for the radiators. How practical this would be I cannot say without knowing the heating circuit. Maybe an additional pump fitted on the return side might help with your current set-up.

Regards

Gray,

Do you have bypass radiator and/or a bypass valve anywhere in the system which might be allowing hot water recirculation back to the boiler instead of being sent to the radiators?

Edit:

Plinth heaters act like an unrestricted radiator as they have no control valves to regulate them.

If you have one in your system you could try slightly closing one of the isolating valves to create some backpressure.

Martin.

Agree it is cavitation at the pump. Water is good at carrying the sound to somewhere else and the large surface of the radiator acts as a sounding board. Add zone valves so you are only heating the rooms in actual use and the pump can be run at a lower level.

I read that heat pump systems are especially prone to problems caused by the growth of organisms such as bacteria and fungi, as well as from magnetic and non-magnetic sludge. Has your system been treated with biocide and inhibitor?

Here is a link:

https://sentinelprotects.com/uk-en/catalog/heat-pump-solutions/air-source/r700-sanitiser-and-biocide/r700-sanitiser-and-biocide/r700-1l/groups/g+c+p+a+nr+view

With regard to balancing of radiators, I have been told by a professional building services engineer that radiators should be balanced by measuring the difference between inlet and outlet temperatures and the valve adjusted to give the design temperature difference.