UFH manifold thumping noises

[Pfanatic]

I am experiencing thumping noises for 10 to 15 seconds as the thermostatic valves begin to open on one of the manifolds in my home underfloor heating system. The system is 6 years old and this is a new phenomenon. I also get a single thump immediately after the demand via the bedroom stat ceases. Both the manifold pump and motorised valve seem to be working OK and there is no air in the system. Any ideas?

[Cds]

Is it single thump or a series of thumps?

[Renewable M]

try turning the pump speed down one, see what occurs.

Is the system open vented?

Then I (and others) may just have an answer.....

[Pfanatic]

It's a series of thumps as the thermoststic valves open and a single thump when the bedroom stat switces off. Also it does not happen all the time, mostly at night when heat demand is high but I noted last night that there was no other demand at any of the other 3 manifolds at the time so I assume it's a high flow issue. I will turn down the pump at the manifold in question to it's lowest setting and see what happens.

[Pfanatic]

Turned the pump down to lowest setting. Still getting seies of thumps when thermostatic valves open and single thump when demand stops. Have also set the electrically operated valve to manually open all the time with same result. This problem is confined to only one manifold out of four.
System has automatic venting at several points.

Turned the pump down to lowest setting. Still getting seies of thumps when thermostatic valves open and single thump when demand stops. Have also set the electrically operated valve to manually open all the time with same result. This problem is confined to only one manifold out of four.
System has automatic venting at several points.

Is it single thump or a series of thumps?

Turned the pump down to lowest setting. Still getting seies of thumps when thermostatic valves open and single thump when demand stops. Have also set the electrically operated valve to manually open all the time with same result. This problem is confined to only one manifold out of four.
System has automatic venting at several points.

[Renewable M]

I could be wrong, it sounds like a flow issue. You have multiple manifolds, probably not balanced, and I wonder what size pump between boiler and manifolds.

Can't say anything else without getting stuck in on the job.

Hope you get it sorted

oh and if it's a sealed system, make sure your pressure isnt too high.