What is causing this UFH rattling noise - any ideas?

[481]

It's coming from our underfloor heating circuit, probably in the ceiling void between the ground and first floors, and is amplified by the pipes passing through a cavity wall into our garage (where they then drop down to the UFH pump and manifold near ground floor level).

It's a rapid rattling sound, lasting about a second, repeated every 20-60 seconds, that starts when the UFH comes on and then dies out over the next 10-20 minutes.

The noise is intermittent and began after 11 years of the system running without any issues. The boiler is a Greenstar HE Plus combi working at 2 bar and regularly serviced. The central heating zone is fine.

Here's a recording (made through the window):

Any ideas what the root cause is?

Thanks!

BTW I can't easily access the place where the pipes pass through the wall, so I want to stop this problem at source rather than by packing/clamping the pipes.

 

[dal5band]

Maybe heat related - when the ufh va!ve opens, is the rest of the system already at full heat ? If so the ufh pipework is suddenly hit with hot water causing sudden expansion. Over the years the pipes have worked lose and hence now grind as they expand. Try turning on the ufh at the same time as the boiler so everything warms up gradually and see if this makes a difference.