On Jan 19, 8:30*pm, AmateurRob
wrote:
Thanks for all the replies - I'll try to address most of them with this
reply:

- System has not been emptied recently (other than a isolating a couple
of radiators when I've re-PTFE'd the rad tails) and I've been getting
rid of air for a few months now - can't believe there's that much air in
there!

- No leaks from pressure relief valve near expansion vessel - there's a
pipe that goes to a drain that's been dry the whole time.

- I've assumed expansion vessel is fine since (a) no water from air
inlet (b) only a small rise in cold-hot pressure change (0.1bar).

- Pressure holds all the time - it only loses pressure when I bleed the
air out.

- Got some inhibitor to add, but I wanted to make sure I'd sorted the
leaks before I added it (and then diluted it with refills). *Might add
that to eliminate the 'hydrogen' gas possibility.

- I suppose boiler leak is a possibility - I'm going to get it serviced
and will find out then.

- I'll re-bleed all the rads again to eliminate as much as possible.

- Can someone tell me what gauge pressure (in the cellar) I should set
so that my ground floor, 1st floor and 2nd floor rads are at the right
pressure (plus it's a Victorian house so the ceiling/height of each
floor is 9 or 10feet)

Thanks,
Rob.

--
AmateurRob

The purpose of the expansion vessel is to take up the expansion of
water when the system warms up.
You should see a rise in pressure as the system warms.
When it cools to it's initial temperature, it should return to the
initial pressure.
If the pressure is less after every heat cycle, you are losing water
somewhere.
If this is happening, eventually after a few cycles it will get to
zero and then below zero and you will get air sucked into the system.
This is the classic sign of pressure vessel problems.

Have your tied a plastic bag ove rthe safety valve outlet to check if
it's coming from there?
This is where the water escapes in 99%of cases (due to expansion
vessel problems)
You can't tell by just looking, the water comes out in drips and may
evaporate especially as it's warm.

For every foot head of water you get 0.4436 psi of pressure.
So, you will get a pressure difference in you case of around 12 psi
between the highest and lowest parts of you system (when the pump is
not running).

15psi = 1bar approx.