Underfloor Heating 0 bar pressure

DettaWalker

Hi,

We've been building an extension with water based underfloor heating. We have two loops, one for the dining room, one for the kitchen. There's been problems with the system start to finish. We had to put in a heat exchanger to get it to work, then when it still didn't get hot much we had to change to a pressurised system and upgrade the pump. But apart from the first few days, the system never managed to sustain pressure. They've topped it up twice now to 1.8 bar, but every time after a day or so the pressure goes back down to 0. 
I'm being reassured that it shouldn't be due to a leak but I'm not sure what to believe anymore. We put click vinyl down so don't know whether we would even see a leak if there is one. And I'm certain the pressure shouldn't be 0. Any ideas on what I can do? I've informed my builder but this has been a headache for two months now.

Rodders53

UFH pipework should be fully pressure tested before the floor screed is laid and that repeated after (in case a pipe get's nicked or damaged during the screeding process).

Losing pressure = most likely a leak or an over-pressure situation where the expansion vessel doesn't do the job properly (too small, failed diaphragm, not inflated correctly) and the over-pressure relief valve operates to let out water until the pressure drops then closes (but it may never reclose properly until someone comes back to reseat it and re-pressurise).

1.8 bar seems very high to me for 'cold'. 

We need much more detail about the system to comment accurately.  What is the boiler? Fuel type? Heat exchanger that you mention? UFH manifold, pumps etc.,.
Makes and models plus pictures... including any expansion vessels, mixing valves, pressure relief valves.

Getting the installation manuals of the parts you have, reading and understanding the makers recommendations about pressures set, pressure vessel sizes cf UFH loop lengths etc.,. may shed some light on any basic installation errors?

DettaWalker

Hi Rodder53,

thanks for your response.
The system was pressure tested at 1.5 bar when laid (for like half a day) - I've read that it should be tested to 5 or 6 bar but that's an opinion on one website, so not sure how necessary this is.

After the screed was laid I think it may have been tested again, but I don't know for sure. 
The boiler is a WorcesterBosch Life 8000 30kw. 
Heat exchanger (which is apparently now obsolete that we switched to a pressurised system) is a:

Stainless Steel Plate Heat Exchanger NORDIC TEC Ba-12-30, 65kW, 30 Plates, 3/4”

I'll take pictures of the rest of the system in a moment. 

Now that the system is cold - it is at 0 bar pressure (don't know if that's normal or not - my plumber said it should be around 1 bar , no more than 2 bar under full operation). 

With expansion vessels and pressure relief valves, do you mean the big vessel that's used to pressurise the system?