Pressure relief valve on closed system water heater

[organicguy]

I have have a closed system hot water immersion heater with a pressure vessel filled by a variable speed pump.
When the system heats up the pressure relief valve blows off and runs for several minutes dumping most of the hot water.
Is it just the valve knackered or could it be something else/

TIA
OG

 

[sjt01]

Sounds like your expansion vessel needs attention. It might need repressurising (should be instructions on the web) via the tyre valve, or if the diaphragm has failed and water comes out of the valve, a new expansion vessel.

 

[organicguy]

Thanks

 

[milkloss]

As the pressure reduces it might be encouraged to boil off more.... one of those self fulfilling thingies.

 

[organicguy]

Just checked the expansion vessel, no water , pressure at 2 bar, said it should be 3 bar so pumped it up a bit.
Now thinking that it will make it worse !
Looks like relief valve which is 90 C 7 bar could be knackered