Daughter bought a house last year with a recently fitted combi boiler. Just before Christmas, she complained about the bathroom being chilly and as the top of that rad was cold, I bled it. Resulting in no heat or hot water! I did a crash course on instruction books, realised the pressure was below the one bar recommended and re-pressurised the system to the recommended 1 -1.5 bar and everything was fine.
The pressure dropped below one bar again yesterday. No-one's bled anything in between and all the rads were hot to the top. Am I looking at a leak?
As an aside, how are these systems filled initially as the mains pressure's above the recommended maximum 1.5 bar and how's inhibitor put in?
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I have two combis - one at Iffy Towers and one at the caravan.
The pressure varies a bit in use is both, and tends to read highest when the central heating has been on an hour or two.
If it keeps on losing pressure, the chances are there is a pin prick leak somewhere.
As well as the pressure dropping, you are also losing 'coolant'.
Tell the daughter to keep a careful eye out for damp patches on walls and ceilings.
I don't know if there is a cleverer way of finding a leak.
Last edited by: Iffy on Tue 11 Jan 11 at 11:57
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I would just re-pressurise and keep an eye on the pressure for a few days. You might be lucky. You could have just lost air and not water.
The systems are filled through the filling loop, just as you added pressure. It takes a few minutes so you just have to keep your eye on the pressure gauge.
Initially the inhibitor can be put in a radiator before the first filling.(Or rather after the cleansing flushes.) In an existing system you need to drain off a few litres and then add to the highest radiator - either through the bleed valve or by removing the blanking plate opposite. Then re-pressurise.
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chances are its just settling down after your last bleed.
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>> re-pressurised the system to the recommended 1 -1.5 bar and everything was fine.
>> Am I looking at a leak?
Could be, but they need repressurising occasionally anyway. Check weekly.
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One thing to check first is the pressure reading when the system is at its hottest. It should read about 2.5 bar. If it gets to 3 bar then the pressure relief valve will open and water will dribble out through the relief pipe. When the system cools you will have lost some pressure.So you then pressurise the system and the cycle repeats and you wonder why you keep losing pressure.
This can happen if the expansion vessel which is inside the boiler has failed or itself has lost pressure.They can be pumped up with a bycycle pump.
Another reason is that your heating system contains more water and therefore has more expansion than the vessel within the boiler can cope with.( see first paragraph) You will find the figures in the installation manual.
In these cases and additional expansion vessel can be tee'd into the heating circuit to cope the extra capacity of a larger heating system. they are not expensive.
If it is neither of these, then you have a leak somewhere, maybe just a compression joint somewhere or a leaky radiator valve.
Hope this helps.
Last edited by: MrTee43 on Tue 11 Jan 11 at 13:49
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Worth finding out if anyone turned any radiators on as when the pressure on mine dropped off after I bled three radiators, I re-pressurised it, was fine for a day, then I turned on two other radiators and it dropped again. Its not a problem, you just have to know how to sort it.
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>>Another reason is that your heating system contains more water and therefore has more expansion than the vessel within the boiler can cope with.
Thank you Mr T. I think I'm beginning to understand these systems.
It's an older house and looks like just the boiler was replaced (and hot water cylinder removed), so the radiators probably have a larger capacity than modern ones. I was surprised by the size of the pressure vessel, it seemed about the size of an A3 envelope, at least I presume that's what the red panel was tucked up the inside of the boiler housing. Previous ones I've seen look more like a calor gas cylinder.
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As per Mr T's post, if the pressure rises quickly after start up, and the relief valve opens, then, it's likely that the diaphragm in the expansion vessel has failed.
The gas which was behind the diaphragm escaped into the system, and collected at the highest points. Then, when you bled the gas out, the system has become effectively solid with no capacity to accomodate thermal expansion.
If your boiler is installed somewhere out of sight, the good news is that you can simply fit another expansion vessel in the system near to the boiler instead of stripping the boiler down to replace the one inside.
When the expansion vessel on our combi failed, I fitted a generic expansion vessel teed off from the return pipe from the radiators.
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Another central heating question - Iffy
