In article .com,
"Robin Houston" writes:
I've got a combi boiler (Saunier Duval Thelia 23). The pressure in the
CH system is too low (about 1/2 bar, judging by the inaccurate gauge).
In the past (i.e. last year) I've refilled it via the filling loop with
no problems.

Now, however, I turn the filling valve and nothing happens. I can't
hear it filling, and the pressure doesn't increase. If I disconnect the
other end of the loop from the boiler and turn the valve, water comes
out at (what looks like) decent pressure, so I think the filling valve
(the one you turn) is okay. (This morning when I tried it, it *did*
fill for about ten seconds before it stopped.)

What's the next thing to look at? Is it likely that the one-way valve
at the other end of the fillin gloop is sticking, and if so what can I
do about it? (Would I need to drain the system and replace the valve?)

Are you in one of the areas where your mains water pressure has
been reduced (London, mainly)? Can you easily stop the water flow
by pressing your thumb on the end of the outlet (in which case the
mains pressure is probably too low to refill the system).

You could try refilling in the middle of the night when the water
pressure tends to be highest as the demand is lowest.

--
Andrew Gabriel