dealing with underground pipe leak

Hello. I have a Camray 5 boiler, one year old. On installation, it kept dropping pressure. The plumber who fitted it searched for a leak and couldn't find one (this is a seventies house that needed renovation (ie new boiler/rads/pipework upstairs). He concluded that it must be a leak in a pipe buried in the concrete floor - if it's leaking down/out it would explain why we couldn't find any tell-tell damp. He sorted it with the RadSeal stuff (can't remember the name. It took two goes, and we've had no probs since).

Two weeks ago, another plumber fitted a pressure regulator on the mains pipe. He checked the boiler pressure - 2 bar. Ten days later, the pump fried- no water pressure at all. He reckons the old leak has blown. As we can't find any leak, he reckons we'll have to repipe the whole ground floor - which seems incredibly expensive/invasive, and want to be sure it's the only option.

He didn't think it was a good idea to try the sealing solution again. Any ideas? At the moment, we're losing one bar every 24 hrs - and I'm just assuming this is a leak, despite no evidence of water. Also, am I OK to keep adding a bar of water to a closed system every day? I don't want to rust the boiler!

I'd be very grateful for any advice - I don't want it to get worse over Christmas! Many thanks.

2 bar is too high. If you have an underground leak you should have some evidence of water showing in the concrete. I would use Wynns auto leak sealer, it's available and it works. If the sealer works, it's unlikely to be an underground leak.

Lack of water pressure does not fry pumps. Lack of water does. his plumber is making unfound statements, get someone else.

Try leaving the system cold (yeah, I know, but that's hard luck if you want to sort the problem) and look for leaks on rad valves.

It's no good worrying about adding a bar as this depends on the size of the system.

Many thanks. Originally, it was set for 1.5. The plumber who fitted the pressure regulator last week raised it to 2 bar, so am thinking the rise in pressure blew the previously sealed leak.

Just to clarify - the pump fried through lack of water - it had all gone - which again I find hard to believe is through a leak in the screed. We'd be afloat, surely?

Really, I just wanted to check that it's OK to use Wynns for a third time (last two times were twelve months ago). The latest plumber didn't think it was healthy for the system. All the rads are brand new/checked for leaks, but will certainly check when system is cold/family are out.

ALL THE WATER HAD GONE?????????????? There's someting seriously wrong, and you need someone competent. Is this a combi, system, or standard boiler?

It's an external combi. I'm only going on what the plumber was muttering to himself (I really hope *you're* not my plumber because I don't want to paint a bad picture!) He did find the burnt out pump and replace it/instruct me how to raise the pressure. It's the talk of repiping the ground floor that alarmed me, plus the thought that the boiler might kick in on timer one morning over xmas, only for an overnight loss of water to fry the pump again.

I'll see if Wynns will fix it. Failing that, I'll just burst into tears. If it is a leak, I just don't see how we can lose a bar every 12 hours without some damp patches rising through the screed.

You can lose 1 bar every 20 minutes into screed and not find any wet patches.
I daresay Wynns might be ok but why not use the leak sealers sold for heating systems? I don't know of a difference, except that the CH system volumes are higher, but there might be.
I'd add more leak sealer. It doesn't seem to do any harm - never heard of a problem, and if it works surely it's worth ££. Have known 3 doses be needed.

I can't see what you have there so this is generally speaking:>

If you want a proper job renew the lot as your plumber suggested

Say you were to find the leak and repair it. You have more copper pipe under concrete so how long will you have to wait for the next leak?

Use your radseal stuff if you need a temporary repair but dont expect it to last forever

It should be able to withstand 3 bar. If it cant it's not up to the job and needs replacing

ChrisR, Radweld and Wynns are more expensive than the CH sealers, probably because they are sold in small quantities. I have used all three, and the CH version seems to be a gloop that takes a long while to work. Radweld is a resin that sets quickly on contact with air. I have fixed a 5 drip/second leak in 30 mins with it, in a combi boiler. Wynns carries a lot of tiny fibres in suspension, as they try to escape through holes they block it up. Air may have some action on it too.

I had a leak somewhere in the system earlier in the year, pipes in a concrete floor and constantly having to bleed the radiators, sounds of air in the pipes. There were no signs anywhere, so plumber replaced hot water tank saying it could be perforated, still had to keep bleeding.

Despite water not showing in floor or bottom of walls but everything else having checked out, we eventually went ahead and had the system repiped, since when there has not been a scrap of air in the system anywhere and the pipes are silent.

Despite having being told that if there was a leak in the concrete floor it would normally rise and show, as one of the radiator pipes was cut at ground level we actually watched the water from it drain away downwards, so no evidence does not always mean no leak.