Combi boiler – faulty pressure gauge or water leak?

31 Dec 2009
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United Kingdom
I don’t know if my combi boiler and system (a) has a water leak or (b) just has a faulty water pressure gauge. The gauge reads 0 bars when the boiler’s not being used and has cooled down. It reads 1.5 bars if it’s running. The boiler appears to work fine (hot water & heating works) even though the not-being-used water pressure is zero.

Any ideas?
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Have you tried repressurising the system back to 1 bar when cold?
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Have you tried repressurising the system back to 1 bar when cold?

Yep. The gauge acts oddly when I re-pressure it. Until recently I would put in some water, stop the water going in, and the gauge would rise slowly afterwards - taking 10 minutes to rise by a bar, until finally it would stop rising. i.e. the gauge seemed to take 10 minutes to catch up with the real pressure.

Now if I fill it, the gauge reacts quickly but the water will stop going in before the gauge even reaches 1 (at around 2/3 bar) - the change in sound indicates that the water isn't flowing in anymore. If the boiler's left off, the gauge pressure will drop back to zero in an hour. If we're using the boiler, it will go up to 1.5 bars and stay there.

Could a boiler even work if the pressure is really zero when cold?

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