Screed just laid, UFH pressure increasing

[chris8]

Hello all,

I've just had builders lay 65mm sand and cement screed on my wet underfloor heating pipes. Following a successful overnight pressure test, the UFH remained pressurised at around 4.5 bar as the builders began to lay the screed.

I've just looked at the gauge on the manifold and I can see it's now 9.2 bar a few hours after the builders finished.

I'm guessing that this large increase in pressure is due to the elevated temperature of the screed curing.

I'm now a little concerned that the pressure may continue to increase above the manifold's stated limit of 10 bar.

Unfortunately, the manifold is located in the middle of the screened area so I don't want to go and release some pressure unless it's absolutely critical.

Does anyone who has seen something like this have any advice or reassuring words they can share?!

Thanks!

Chris

 

[DetlefSchmitz]

Are you using binoculars? Pragmatically you could take some regular observations to see if it has stopped rising. If so, all well and good.

 

[chris8]

Haha I can peer through a window at the back of the house! Making some observations over the next couple of hours is a good idea.

 

[MeldrewsMate]

Water being virtually incompressable means that even a modest increase in pressure with no expansion volume will cause a significant increase in pressure. Ironically, if you have managed to bleed most of the free air out then the bourdon tube inside the pressure gauge probably contains the most expansion volume!
Good advice has been given re: making regular observations, but if the time comes that you need to bleed off some small amount of water then you may want to have some crawling boards at the ready. Fortuitously the cool weather will help to keep down the screed temperature, and open windows at night will both help to keep it down and allow dispersal of the free moisture.

 

[MeldrewsMate]

Haha I can peer through a window at the back of the house!

...as long as it's your house.

 

[chris8]

Thanks for the reply. An interesting point about the air in the pressure gauge!

The pressure seemed to be increasing by around 0.1 bar every 10-15 mins, and about an hour after posting it was close to 10 bar. The temperature inside the room had also increased over the evening from around 18.5°C to 20°C, despite the outside temperature dropping.

I stopped looking at the gauge at that point because there was nothing I could do without risking damaging the screed. I will check again this afternoon and see if it's gone down at all. In hindsight a safety pressure relief valve set to 9 bar might have been a good idea.

 

[chris8]

...as long as it's your house.

 

[chris8]

OK, just checked and the gauge is now reading about 7 bar, so hopefully it'll continue to fall over the next couple of days until it's back where it started (4.5 bar). Panic over!