OSO unvented cylinder

[pmplum]

Hi
I have customer with a 330 litre OSO Invented cylinder with water coming from the cold water expansion valve.
My question is these cylinders have an internal expansion “bubble” , can they fail ?
Tried draining it and refilling to recharge the bubble
Checked hot ware temp and it’s at 60 so not over heating
Question is about the internal expansion bubble
Thanks

 

[Gasmk1]

i thought oso vessels were external ?

 

[pmplum]

i thought oso vessels were external ?

This one on the 330 litre is internal
It’s about 8 years old

 

[SavageW]

The relief valves are notorious for passing once they have discharged,you could have recharged the bubble correctly just the valve has not reseated