A friend's combi-driven CH system is losing pressure. After refilling,
the pressure drops to zero within two hours. No obvious leaks upstairs,
downstairs or in the unheated cellar where the downstairs pipes are
He thinks it must be leaking under the relatively recent
Is that a reasonable conclusion?
If so, how can the leak be pinpointed? He's hopeless at DIY and I'm at
the other end of the country but in general terms, is there a way to
prevent the entire floor being dug up in the search?
He's had a plumber in who pumped in some leak sealer to no effect.
What should he do next?
And can anyone recommend a reliable plumber in E17 / Walthamstow? (He's
away for Xmas anyway so he's not requiring an emergency call out on Xmas
Thanks for any pointers.
In case everyone else is down the pub, I offer this:
Turn off all lock shield valves on all radiators (or if he knows the
pipe routing, just on the first rad on each leg) then repressurise. If
it still leaks, the leak is between the last bit of visible pipe(s) and
one or more of the rads on one or more of the legs.
If it doesn't leak, open lockshield valves in some kind of sensible
sequence until it does leak - then the leak is between the one just
opened and the one just previously opened.
This advice is worth exactly what you've just paid for it.
It's possible although unlikely.
Mine does the same, but it's the blow off valve ( the high pressure relief
thing) that is causing it - I've purchased a new one and fitted it but the
problem remains the same, however, in the past 2 days I have managed to keep
it pressurised and I did this by accident.
I turned up the roomstat from 20 to 25 degrees, this made it too warm but
the thing stayed full, so to compensate, I turned down the heat setting on
the boiler....I've no idea how this 'fixed' it, but it's not required
refilling since Wednesday, whereas before then it lasted no longer than an
hour or two
Ask him to check the copper outlet outside next time it loses pressure,
he'll probably find that his hot water is not far away.
Agree with all that.
Also, if there has been a recent extension then the current expansion tank
may not be large enough. I havn't had a relief valve fail (and they usually
fail if they leak) since I added a bigger tank.
As others have said, there may not be a conventional leak at all, but the
system may be losing water through the PRV (pressure relief valve).
Your friend can check this by locating the pipe which goes out through the
wall from the PRV, and placing a container under the end of the pipe to
catch any water which comes out.
If water *is* being lost through the PRV, the valve *could* be faulty - but
it's more likely that it's simply doing its stuff and preventing an
excessive pressure build-up - as can happen when there's a problem with the
The expansion vessel contains air (or sometimes nitrogen) which is separated
from the water by a diaphragm. When the water in the system gets hot and
expands, it compresses the air in the expansion vessel, causing just a
modest increase in pressure. However, if the air leaks out and the expansion
vessel is completely full of water, any expansion causes a much higher
increase in pressure - with the result that the PRV opens and releases it.
When the system cools, the pressure is all lost.
If this is the problem, the expansion vessel will need to be re-charged with
air or - if it is completely shot - replaced.
Thanks for all the replies and thanks for your explanation Roger - that
really helped to clarify what Ed has listed in the FAQ.
He's taped a bag over the pipe tonight and will report back on any water
Another place to look is under the caps of lockshield valves. Water
can leak through the gland when warm but is evaporated by the heat.
When I converted my system to sealed operation I changed all of the
valves and there were three of the originals that had leaked as
evidenced by staining and gunk around the upper part of the valve.
There was nothing on the chrome body part.
Ah a sensible post on this topic from me - had a similar (but less
noticeable) problem with my systeme wher a bathroom towel-warmer type
rad was leaking from the TOP joint ... never noticed it until the powder
coating blew ...
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