The boiler is a Chaffeteaux Britony 80 Combi. The expansion vessel
loses all pressure quickly.

After suspecting the vessel, I depressed the valve's plunger and found
that no air came out. I pumped it up with a bicycle pump so that the
pressure guage read 0.7bar more than it was before. An hour later, the
pressure had dropped back to where it was, and no air came out of the
valve when I depressed the plunger.

No water seeped from the valve when I depressed the plunger. I'm
wondering if the valve could be the culprit. Are these the same valves
that they use in car tyres? Is it as simple as going to a car spares
shop and asking for a tyre valve?

Thank you,

Jake

In an earlier contribution to this discussion,
Jake S wrote:

The boiler is a Chaffeteaux Britony 80 Combi. The expansion vessel
loses all pressure quickly.

After suspecting the vessel, I depressed the valve's plunger and found
that no air came out. I pumped it up with a bicycle pump so that the
pressure guage read 0.7bar more than it was before. An hour later, the
pressure had dropped back to where it was, and no air came out of the
valve when I depressed the plunger.

No water seeped from the valve when I depressed the plunger. I'm
wondering if the valve could be the culprit. Are these the same valves
that they use in car tyres? Is it as simple as going to a car spares
shop and asking for a tyre valve?

Thank you,

Jake

Did you do all this with the water system cold, and unpressurised? If not,
you need to do that.

To test the valve, re-inflate it to 0.7 bar and then spit on your finger and
wipe it over the end of the valve. A bubble will form if the valve is
leaking. If the vessel loses pressure, but the valve *isn't* leaking, the
vessel itself must be duff - in which case, I can't understand why no water
comes out of the valve.
--
Cheers,
Roger
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