CH losing pressure - but very slowly (long)

[JoeJoe]

Had a Saunier Duval combi boiler (non condensing) fitted ~4 year ago as part of a large extension. The existing pipes and radiators were left untouched, but quite a few new ones were added to the system to cover the new rooms that were added. It is a single zone system, so all the pipes/radiators are now part of the same circuit (or whatever you call it).

I will try to describe the problem giving as much detail as possible:

- The pressure of the system is dropping all the time. Initially I had to top it up every few months, but the frequency has gradually escalated. Last winter it was down to once every couple of weeks, so far this year I had to do it every couple of days or so. Not ideal, I know, but see below why we decided to try and live with it.

- I set it to around 1.2-1.4 and top it up again when it drops to 0.7-0.8. The system cuts off when it goes down to 0.6 (it has a digital display).

- The pressure seem to only drop after the heating has been running for a while, and remains pretty stable for a long time (days/weeks/months) if no heating is used.

- The pressure seem to drop almost immediately (i.e. after running the heating once) to 0.9 or 0.8, but then stays there for a while (again, days/weeks/months) until eventually it drops to 0.7 or so where I have to top it up again.

The house is a 2 floor detached with suspended floor that can be easily access from below - around 1m height under the house..

My obvious suspicion was a leak, however:

- There is no noticeable sign of it on any of the ceilings

- Unfortunately all the new part of the house (around a 3rd of it) is inaccessible from below at all, and has solid oak flooring that I would rather nor rip...

Any idea what is going on here based on the above? Anything I can try before I go under to inspect the accessible part? It is horrible in there...

May thanks in advance.

PS: The boiler and new pipes/radiators were fitted by the most incompetent plumbers I have ever come across (and I have done up 10+ houses as a side business over the last few years, so I have seen many pretty closely). Ass the builder we hired brought them with him we haven't had much say in the matter, and most of the problems only became apparent late on. Every single thing they touched failed within days or weeks at most, and we were so concerned that we ended up calling Corgi who sent an inspector to verify that it was at least not dangerous. It wasn't apparently, but they were so lazy that they left 1m of 15mm gas pipe that should have been upgraded to

22mm along the way that they had to come back and do.

[Mike Buckley]

We had exactly this after a recent move to a combi from a thermal store, this meant running the CH at mains pressure, so I was pleasantly surprised when nothing leaked.

Well, for two weeks.

Then the pressure started dropping, it needed a daily top up. We have wooden floors downstairs and upstairs mainly laminate. I was dreading ripping up any floors but closer examination of the downstairs it looked like the pipes run in the walls and not the floor at all. Three days later and directly above the TV the very recently plastered ceiling turned brown. Oh well - easily fixed - ripped up the laminate in the en suite to find that the towel rail was just plastic fittings and one was leaking. Took it apart, cleaned it and re-assembled and it's been fine since (although I haven't put the laminate back just in case). Might be worth checking any plastic fittings if you have any, sods law it'll be in the floor though.

[Ronald Raygun]

I suspect he hasn't looked at the relief outlet. The symptoms, especially the fact that it has been gradually getting worse, and that it then happens after the first heating) strongly suggest that the expansion vessel has lost its air, so that when the heating goes on, the pressure caused by the expanding water causes the relief valve to operate. Once it cools down, the lack of air in the expansion vessel means there's nothing to keep the pressure at normal levels, so it drops.

The usual fix involves using a bicycle pump.

[JoeJoe]

What amount of water am looking for for such a leak? a cup-full? litters? a few drops?

When if the best time to try and spot it? Top the system up, turn it on, and then look?

Obviously there is a leak. I assume you have made sure the safety/ relief valve is not leaking. Outlet from it normally goes outside the house. It will be by the boiler. Check there are no drips from this.Check for wetness on carpets under radiators.

If you can't see the leak, it's obviously in an awkward place. The most likely being where the pipes are buried in the floor. Cement will attack copper pipes unless they are protected. Normally this shows up as a wet patch but if you have wooden floors, these might conceal it. Unfortunately you have to go round &find out where the leak isn't. Which will leave just few expensive to check places where it must be. Make sure it's not the boiler itself leaking, sometimes this is not immediately apparent.

[JoeJoe]

Anything I can do myself to check this, or should I phone someone to look at it?

>

[RobertL]

I suggest:

(1) drain water until the pressure stops falling, then (2) pump the accumulator with air up (bike pump or car foot pump) to about 0.5 Bar, then (3) fill with water back up to the usual working pressure. i expect others will be along later with the correct figure for the 'slack' pressure. if this fixes the problem then all is well.

Robert

[Ronald Raygun]

Find the relief outlet. Normally the pipe goes through the outside wall and protrudes a few inches form the wall. When the relief valve operates, you should see a drip from there, but it might not be obvious. When the system is cold, put a dry bucket under it. Then pressurise the system and turn the heater on for an hour or so. Then see whether there's any water in the bucket.

[Richard Russell]

Indeed, that's my guess too. The "obviously a leak" diagnosis is more than likely completely wrong.

Richard.

[newshound]

For the pressure to drop visibly, you must be loosing cupfulls (cupsfull?).

But if you tape a poly bag over the overflow pipe you will easily spot fractions of a teaspoon.