Combi boiler constantly losing pressure

leannejj

Hi all

Hoping someone on here can help me as I'm pulling my hair out! Woke up on Thursday morning with no heating and no hot water. The boiler pressure was on 0. I didn't check the pressure before bed the night before (as there were no signs of a problem) but the heating and hot water was working fine. Within 8 hours, we had nothing.

Engineer came and said he suspected the PRV (although the wall outside wasn't wet) and that he would order a replacement and come back on Tuesday (yesterday) to fit it. He topped it up before he left on Thursday and put a bag under the PRV pipe outside to see if it was letting water out. Between Thursday and Tuesday, boiler pressure remained steady with no need for adjustment and the heating/hot water worked perfectly. The bag outside also remained empty.

Yesterday the engineer came back and fitted the new PRV. Since then, I thought the pressure had dropped slightly, so when the boiler was cold, I topped it up to 1 and decided to keep an eye on it. That was at 9.30 this morning. Now 4 hours later, it is just below 0.8.

What could the problem be? I didn't think it was the PRV but he changed it anyway. I know it would suggest a leak somewhere, but how comes the pressure was steady between Thursday and Tuesday? Now, only since it's been tinkered with, it's unstable again! I've felt all the pipes around the radiator and there are no wet patches. Also there are no water marks on floors or ceilings. What else could it be?

Thanks in advance!

macman

Make and model would help. Your RGI is not competent. If the PRV is not venting, as evidenced by the bag that he placed on it, then why change it?
If not the PRV, then it will either be the EV (possibly failed or needs repressurising), or you have a leak on the CH circuit. He should have checked the former, it would have taken just a few minutes. If not that, then it's the worst option, you may have a leak in a concealed or buried section of pipe.

leannejj

It's a Vaillant Ecomax. I was hoping it wasn't a leak as the pressure didn't drop at all between Thurs and Tues. Is that possible even with a leak? I asked him to check the expansion vessel and he said it was fine. How can I find out where a leak is if there is one? I have felt all around the radiators and can't detect any wetness there at all :-(

marleyboy

Ensure all the valves on the radiators are closed tight, just loose enough to let the air escape will drop the pressure via the CH.

leannejj

Apologies for the DIY dunce question, but is that where the radiator joins the copper pipes or the bit at the top where you bleed the radiator from? Thanks for your help

Grenage

He'll mean the bleed valves; don't do them too tight, just tight enough.

Start looking around for damp patches on ceilings and in corners, it could be a slow leak, and it could be absolutely anywhere the CH pipes run.

chappers

ahh the foibles of the combi boiler.
I had a similar issue. Had a pressure drop so topped up, the same thing happened the next day, so on the third day I did the bag over the PRV thing and that remained dry. So assumed a leak checked everywhere obvious and topped up again expecting to have to make further investigations, but the pressure remained OK for nearly 3 weeks before dropping again. Knowing it wasn't a leak I finally got my mate to have a look at it and sure enough it was the EV.
Considering your man changed a perfectly functional PRV I would be wondering if he checked the EV properly, if at all.

leannejj

Thanks for the suggestions. I have looked everywhere I can think of (without ripping up carpets etc!l) and haven't seen any signs of leaks but I will to check every day in case, as you say, it's leaking slowly. I'll also check the valves as suggested above.

Would you be surprised if I told you the engineer was from one of the biggest gas providers in Britain (there's a clue...!). Think it's going to require another call out. I had to ask him to check the EV, so I'm not sure whether he did or didn't know how to, but from a bit of googling, it was thing I'd thought of straight away, rather than the PRV. And I have no idea about boilers or any form of DIY unfortunately! Here's hoping, if I call them out again, I get someone else!

Grenage

BG are notoriously pants.

kev25v6

Water can be leaking inside the boiler into the hot pipes and evaporating off so you won't see a puddle but there will be a stain on the pipe work to see.

macman

As already stated, the leak If there is one) may be on a pipe run under the floorboards, or wherever the pipes run, so it's no good just checking at the rad connections. There's no quick way to find this, which is why you first need to rule out the EV.
Get in a competent independent local RGI who can do this basic fault finding, and ask BG to refund the cost of replacing a perfectly serviceable PRV.