In article ,
Roger Mills writes:
On 05/02/2019 19:57, Chris J Dixon wrote:


I have a condensing system boiler. Last winter I noticed that it
seemed to need the pressure topping up regularly, but no leaks
were detectable.

During the summer, where it was still in use to heat my
unpressurised hot water tank, no topping up was necessary.

Back in the heating season the issue has returned.

In describing the situation it occurs to me that the difference
is that the hot tank is next to the boiler, so is only raising
the temperature of a small volume of water, compared with the
whole radiator circuit, which latter would thus cause more
expansion.

Chris

Yes, it looks like your system has *some* expansion capacity but not
enough to cope with the whole system getting hot. Re-pressurising the
air in the expansion vessel will likely fix that.

Can you get at the air valve on the expansion vessel? If so, bleed
enough water out of a radiator for the water pressure to drop to zero.
Then check the air pressure with a car tyre pressure gauge. It needs to
be somewhere in the region of 0.7 to 1.0 bar (10-15 psi). If it's a lot
lower than this, top it up with a car tyre pump. then use the filling
loop to re-pressurise the wet part.

I did this. I measured the water extracted by running it into a
2 litre pepsi bottle. It took two cycles of bleeding water out
and pumping up to get 2 litres out (and therefore approx 2 litres
of air in the expansion vessel). I had expected to need to get
more than that in an 8 litre expansion vessel, but 2 litres
returned the system back to normal pressure range during operation.

--
Andrew Gabriel
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