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combi boiler pressure loss?

baxi 80e combi losing pressure. Only used to lose pressure with heating on. Used to have to top up every couple of weeks, now every 2 days, 1.5 bars to 0.3 in 2 days.
No visible leaks upstairs so had plumber round to check below floorboards and found no leak.
Topped up to 1.5 bar shut off flow and return to rads.
Pressure dropped to 1.1 over a few days of using hot taps then has remained at 1.1 for several days.
Just turned flow and return back on and the pressure remained at 1.1.
At a loss to work out whats going on.
No discharge out of over flow (put condom over it).
Boiler serviced a few months ago engineer said to try fernox leak sealer but no joy.

gameoverman
April 2009

Baxi Heating, Home Heating Systems Boiler Pressure Baxi Heating

We had a similar problem - a couple of radiators had minor leaks. However as leak only occured when radiator was on the water evaporated before it caused a damp spot. We only found the issue when we took a radiator off the wall to decorate and there was a rusty water mark on the wall. We then checked all the radiators and found the same/ similar on one other. Plumber fixed the radiators and the boiler now holds its pressure when the heating is on.

Samstan
December 2009

Thanks Keith, but there's nothing coming out of pressure relief valve or anywhere else visible, as I said had floorboards up downstairs but plumber couldn't see any leak and was pretty adamant there wasn't. Could he of missed somewhere I'm thinking? as it can't be upstairs as with the volume that's going surely we would notice.
Don't know if it's possible but could the boiler be evaporating the water?

gameoverman
April 2009

check the pressure relief valves not leaking water,its a 15mm pipe from the boiler through the outside wall into drain onto the ground.
check all rad valves beneath the control knobs for leaks.
check behind the drop down facia lhs for leaks.

keith brown
April 2009