Thumping manifold, bouncing flow meter

[Wayne74]

I have a Rehau underfloor heating system on the ground floor only of my house. Every so often, the manifold makes a knocking/thumping noise. When I look at the flow meters I can see the one that's making the noise and the little ball in the flow meter is bouncing up and down (so the water level is bouncing up and down, obviously). Could this be air in the system? It only does it when there is demand on that particular loop (the hall, so there's often demand as the temp changes due to the front door being opened). If I turn the pump speed down it simply changes the tempo of the thumping! Any ideas? The flow meters are beginning to look opaque so I guess the system needs cleaning out anyway, but the thumping has occurred on and off since the system was installed (now 5 years old).

 

[Daveplumb88]

Sounds like (boom-boom) you need to replace the TRV head for that particular loop. I've had it happen briefly when the head gets to a certain position while closing down (they can take a minute or two), but not constantly. Have you also tried tweeking the flow limiter &/or the flow/return blending valve?

 

[Daveplumb88]

Oh, and I wouldn't worry too much about a bit of visible discolouration in the flow limiter glass. Though if you've rads upstairs, have you got a magnet/filter on the primary return?

 

[Sparkgap]

Just a thought: used to have occasional thumps on rad TRVs which were due to flow through valve being backwards! Have you checked the valve body to see if it's right way round for flow?

 

[Uheat – Wojtek]

Hi Wayne,

does it just happen to one flow meter?
I've had a customer week ago with exactly the same symptoms at Uponor manifold.
He replaced the flow meters and the noise is gone.

Thanks

 

[Uheat – Wojtek]

Hi Wayne,

does it just happen to one flow meter?
I've had a customer week ago with exactly the same symptoms at Uponor manifold.
He replaced the flow meters and the noise is gone.

Thanks