Expansion Vessel charge

14 Aug 2007
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United Kingdom
When recharging an expansion vessel today it wouldn't hold air pressure so I assume it was leaking into the heating circuit.

When I first tried the vessel no water was coming out valve but there was no air either, I attached my pump and blew a lot of water out but now the vessel is empty but will not hold air.

I would have thought if the vessel was burst I would be getting water from the valve when I push it in.
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Has the valve gone ? I usually change them.

What happens exactly with yours ? You put a pump on it and pump and then when you check it there is no pressure ?

as andy, change the scrader valve. you can get 100 and a removal tool set for about £3 on fleabay.
When I was pumping it up the air was coming out of the air release valve, I closed this thinking it to be the problem, the pressure gauge on front of the boiler then began to rise.

As I say, I had already pumped all the water out the expansion vessel, I then opened up the PRV to discharge the pressure (I was changing PRV)

Pressure dropped, I left PRV opened and continued to pump, after several minutes I rechecked pressure but expansion vessel was flat, no air or water now.

Could the vessel be burst and when I've been pumping it's been it's been going out PRV or into heating circuit.
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Firstly you need to release pressure from and open the heating side when charging a vessel. I think you may have done this in the end but not initially as you said the gauge on the boiler was going up.
If air was coming out of the AAV then it does sound as though the vessel has gone.
Personally I would get a valve and tool from Halfords, swap the valve and then see if you can get pressure into the air side of the expansion vessel.
It is sounding as though it has failed, just the fact that no water came out of it contradicts that.

Was there really system pressure when you first pushed the valve pin?

It does sound as if the diaphragm is punctured but all these tests have to be done carefully to assess the correct situation.


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