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Discuss UFH pressure when running. in the Water Underfloor Heating Installations area at PlumbersForums.net

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Hello

I've laid wet UFH in the new extension (suspended floor) as follows:

1) 3 loops (about 80m each) in the zone.
2) 2 port valves for 3 zones on the flows (UFH, upstairs rads, downstairs rads).

The pressure test indicates no leaks in any of the loops.

When the valve to the UFH is closed, the pressure indicated on the manifold gauge drops to zero over a period of time. The boiler pressure remains at a steady 1.5 Bar. As soon as the valve is opened, the UFH manifold gauge pressure goes back up to 1.5. The zones are operating and heating effectively aside from this.

Can anyone suggest other avenues of investigation or perhaps a theory on what may be happening?

Thanks
 

oz-plumber

Esteemed
Plumber
First option - replace pressure gauge on ufh manifold and see what happens.

If it's doing the same thing, test each circuit individually.
 
D

Daveplumb88

As long as you don't have to top up through th filling loop, I wouldn't worry. It's still connected hydraulicly (?) by the return pipework. If leaking you'd lose all your pressure from whole system. It's a bit of an anomaly that you'd have to see the system to explain (possibly). So, as long as there's no topping up required, best thing is STOP LOOKING AT THE GUAGE, and worry about something else, like what the wife gets up to while you're at work.lol.
 

Dan Masey

Gas Engineer
Sorry to kind of hijack this post. Kind of on point, but when adding UFH to an existing system, does this out a big amount of pressure on the expansion vessel as suddenly the system has a lot more water within it?
 
D

Daveplumb88

As long as the TPR doesn't discharge and you lose pressure/system water, then the existing expansion vessel will and is coping. Pressure vessels can take the pressure, it's in the name. If, however, the system loses pressure through the TPR (guage at 3 bar or thereabouts), then you can just cut in another small vessel rather than paying mote for a bigger one.
 
D

Daveplumb88

I've just worked it out (I'm such a freakin nerd sometimes) and for every 100m of 16mm ØD UFH pipe laid, you add 15.4 ltr..So, allowing for 5% expansion, you need to allow 0.77 ltr of expansion space for every 100m UFH pipe laid.
 

chris watkins

Esteemed
Plumber
Unfortunately Dave it doesn't work like that when sizing vessels, there are a few more things to take account of.
Hope this helps
Heating Vessel Sizing Guide.png
 

chris watkins

Esteemed
Plumber
The above is care of RWC
Static Head in metres = cold fill pressure normally 10M (1bar) so p1 would be 2.
Safety valves are 3 bar on domestic systems so p2 = 4.
e = 90deg C therefor 0.0359
just need C total system volume

Take off what is already there if you like (boiler) and then buy next biggest vessel for remaining.

Nerd's of the world unite.
 
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