System leak

[greentangerine]

My ASHP (commissioned in October) has developed a leak somewhere.

I'm having to top up the system every 30 minutes but no sign of a PRV leak or a leak anywhere else for that matter which leads me to think that the existing CH pipework might have an issue.

Given the amount of fluid I've put into the system over the past few days I was sort of hoping that if there was a leak in the pipes it would have shown up by now but so far nothing. All the pipework upstairs is in the ceiling void and no stains so far on the ceilings. Downstairs is a combination of concrete floor or suspended.

Any suggestions on how to track this down?

I'm still waiting on the installers of the ASHP to come out but there's no leaks around the DHW / Buffer or the pipework they installed and the expansion vessel would be full by now - plus it seems to be working as when I refill it stops at the pre-charge setting. Not sure if there's some PRV inside the ASHP itself.

[Tinbum]

Can you isolate parts off?

[Oldgreybeard]

There should be a PRV somewhere, mine is sat on top of the accumulator, with a pipe running to a visible tundish, so it's easy to see if the PRV is letting by. There isn't one inside the ASHP, I'm sure, as the installation manual for mine stipulates fitting one during the installation. The installers could have put the PRV anywhere, but it must have a drain either going outside or to an existing waste pipe (mine does the latter - the water from an ASHP is never hot enough to cause a problem with plastic pipes).

PRVs letting by seem to be a fairly common reason for apparent leaks/loss of pressure, in my experience. Happened twice at our last house, both times replacing it fixed the problem. Annoyingly they often seem to refuse to re-seal when manually operated (usually by twisting the, often red, cap). I did once manage to semi cure a leaking PRV by manually operating it a few times, I think it just cleaned the valve seat. Unfortunately it started letting by again a few months later, so this wasn't a permanent fix.

[spread-tee]

Are you filling it via a standard type of filling loop that commonly gets fitted to combis? if so how long does it take to represurise from zero to 1 bar. If it is say 30 to 40 seconds that is quite a leak that would show up pretty quickly if it were anywhere but under the ground floor. Have you got reasonable access to the underfloor void? if so I have found leaks before by the sound of dripping if the rest of the house is quiet. An IR thermometer can help find leaks in UFH slabs.

Other than that it is as Tinbum says try to isolate various bits and eyeball everything you can.

Desp

[Oldgreybeard]

Does anyone think that they sometimes tempt fate by posting things?

Last night our underfloor heating didn't seem to get very warm at all. The ASHP was running all through the off-peak period, but not drawing as much power as it usually does, plus it was cycling on and off, which is unusual. By late this afternoon the house was maybe half a degree cooler than normal, so I started investigating.

When I first fitted the heat pump I installed a differential pressure bypass valve, to "short circuit" the flow and return in an attempt to overcome an issue with occasional flow related lock-outs from the ASHP (if it detects low flow it locks out). The differential pressure bypass didn't fix it, so I added a low loss header, and that did the trick. I left the differential bypass valve in place as it was in an awkward place and I thought it'd do no harm to just leave it be. This was about 7 or 8 years ago.

After checking just about everything to try and find the cause of the problem, I took half the airing cupboard aprt the get at the differential pressure bypass valve. Sure enough it was stuck wide open. As soon as I removed the pressure adjustment locking ring and touched the adjuster it clicked, as the spring loaded plunger closed. I've now wound the adjustment right in, so the valve cannot ever open (doesn't need to with the LLH), so hopefully it's now fixed. A quick run up for an hour on battery power showed the heat pump working fine, so presumably it was just being "short circuited" that had caused the problem.

I'm sure I tempted fate by mentioning earlier that valves fail . . .