I switched the central heating on a couple of weeks ago & it has been fine
since until this morning. When I got up this morning the house was cold &
when I checked the pressure at the combi it was low. I topped it up & the
heating came on ok & went back off on the timer. A little while ago I tried
the hot water & only got cold, checked the combi again & the pressure is
down again. I also noticed that the pressure relief valve (?) has been
putting out water probably because I may have overfilled the boiler. Have I
got a leak in the system or could there be some other explanation. It is a
Ferroli combi.

Andy.

In an earlier contribution to this discussion,
gonzo wrote:

I switched the central heating on a couple of weeks ago & it has been
fine since until this morning. When I got up this morning the house
was cold & when I checked the pressure at the combi it was low. I
topped it up & the heating came on ok & went back off on the timer. A
little while ago I tried the hot water & only got cold, checked the
combi again & the pressure is down again. I also noticed that the
pressure relief valve (?) has been putting out water probably because
I may have overfilled the boiler. Have I got a leak in the system or
could there be some other explanation. It is a Ferroli combi.

Andy.

You should have a bomb-like expansion vessel somewhere in the system. Sounds
like this isn't doing its job**. It *may* have a ruptured diaphragm - but
more likely has just lost its air for some reason. There should be a
Schrader valve (like a car tyre valve) on it to enable it to be pumped up.
The air pressure when the system is cold should be about 1 bar (15-ish PSI).
If water comes out when you press the button in the middle of the valve,
it's had it. Otherwise re-inflate it to the correct pressure and see whether
that cures your problem.

** When the system heats up, the water expands and needs to be able to do so
without causing too much pressure rise. The expansion vessel allows this to
happen. If this is not working, the pressure builds up and the relief valve
operates - letting water out of the system. When it subsequently cools down,
the water contracts and the pressure drops to below the required level,
requiring it to be topped up. Vicious circle!

--
Cheers,
Set Square
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On Fri, 08 Oct 2004 16:42:45 +0100, gonzo wrote:

I switched the central heating on a couple of weeks ago & it has been fine
since until this morning. When I got up this morning the house was cold &
when I checked the pressure at the combi it was low. I topped it up & the
heating came on ok & went back off on the timer. A little while ago I tried
the hot water & only got cold, checked the combi again & the pressure is
down again. I also noticed that the pressure relief valve (?) has been
putting out water probably because I may have overfilled the boiler. Have I
got a leak in the system or could there be some other explanation. It is a
Ferroli combi.

Andy.

See SealedCH FAQ

--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html

On Fri, 8 Oct 2004 16:42:45 +0100, "gonzo" wrote:

I switched the central heating on a couple of weeks ago & it has been fine
since until this morning. When I got up this morning the house was cold &
when I checked the pressure at the combi it was low. I topped it up & the
heating came on ok & went back off on the timer. A little while ago I tried
the hot water & only got cold, checked the combi again & the pressure is
down again. I also noticed that the pressure relief valve (?) has been
putting out water probably because I may have overfilled the boiler. Have I
got a leak in the system or could there be some other explanation. It is a
Ferroli combi.

Sealed Heating System FAQ
http://www.makewrite.demon.co.uk/SealedCH.html

Phil
The uk.d-i-y FAQ is at http://www.diyfaq.org.uk/
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