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I have a combi boiler, this one, required to fill in 1.5 BA, 8 radiators, and heated floors in the same system.

I have a pressure loss problem, I lose ~0.3-0.4 every week without visible leakage. I had 2 plumbers and 1 guy from the boiler gas service company.

The leakage wasn't found. The expansion vessel is okay - excluded by both plumbers. The pressure relief valve is ok, the filling loop is ok.

What I did:

  • turned off the floors - same situation
  • checked all the visible pipes and thermostats with napkins - no wet
  • bleed all the radiators after a top-up to get the air only

Maybe crucial for analysis:

  • Once the pressure had dropped to 0.1, I thought it was a significant leakage and drained out all the water through the filling loop, I got 0 BA. Then we found no leakage - we topped up - the pressure started rising immediately from 1.0 and not 0 as was expected.
FreeMan
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Artem Ptushkin
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    You need to become detective - keep splitting the system to find which bit leaks. Then subdivide that bit until you find the source. And if the boiler is losing pressure then there **IS** a leak. – Solar Mike Jan 20 '23 at 10:14
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    Maybe the pressure relief valve is not ok or the pressure is to high and is being depleted by the relief valve. – Rohit Gupta Jan 20 '23 at 11:00
  • @RohitGupta, not PRV definitely, it's dry and not connected to any pipe - I'd see the water. It's for 3 BA but I has never reached 3 – Artem Ptushkin Jan 20 '23 at 14:19

1 Answers1

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My guess is that it's a failure in a heat exchanger. If it's the main one the hot water may get out as steam through the flues (or to the drains through the condensate pipe if your one is a condensing boiler). You may see it if you open the sealed chamber looking for oxidation/scale deposits. If you ask me I bet this is your case.

If it's a combi also the domestic hot water (DHW) one may leak "back" to cold water lines (but in this last case, is more common an unexpected pressure increase, being cold water, usually at higher pressure than heating)

SOHR
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DDS
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