Pressure vessel

Citizenpain

The pressure vessel in my hot press has failed for the 3rd time in 6 years. Well I think it has as it sounds like it’s full of water if I tap it . I assume it’s not normal to last so little time . Any idea what might be causing this ?

John.G

Remove the plastic cover on the end of the expansion vessel and press the valve on the schrader valve with your finger nail, if air comes out its not full of water, if water comes out it obviously is, and will need renewing, if neither air or water comes out then it may just need re pressurising, it certainly shouldn't be failing every couple of years, there are different types of expansion vessel depending on what they are installed for, ie on the heating system or the domestic water system and I think are different colours.

Can you post a photo of it (label etc), you don't say if this is a expansion vessel for your heating system of for a unvented (pressurised) hot water cylinder. If, as you say its full of water then either the pressure relief valve (PRV) on your boiler should be lifting or the temperature & pressure relief valve on your hot water cylinder should be passing water each time the cylinder reaches temperature.

Citizenpain

Thanks , will take a pic tomorrow

Citizenpain

Ok , no air or water escaping so hopefully just needs to be recharged . It’s connected to the Hot water tank

John.G

Its a bit surprising that the temperature and pressure relief valve on the hot water cylinder isn't lifting each time it heats up, what indication did you have previously that the expansion vessel(s) needed replacing?, if you have a pressure gauge anywhere in the system it would be interesting to see its variation in pressure.

Citizenpain

I’ve a gauge at the pump . Shows slightly less than 3 bar.
Previous time i’ve Asked a plumber in when water was discharged externally from the tank or the pump was kicking in when it shouldn’t. The pressure release valve had to be replaced as well

John.G

The expansion volume has to go somewhere, it will be ~ 2.8 litres with a 150 litre hot water cylinder and ~ 5.5 litres with a 300 litre hot water cylinder so if that 3 bar pressure isn't changing with hot and cold conditions then that expansion has to be accommodated or released somewhere.