Boiler over pressurising?

[Wile.E]

My son has a Boulter Buderus Gas boiler and today he noticed water coming out of the vent outside having switched the heating on. I assume it is the pressure relief valve operating so I asked what the boiler pressure was....5 Bar! No wonder it was venting! So once it was cold and boiler inactive I asked him to bleed the nearest rad (bathroom) and he reduced it from 2.2 Bar to 1 Bar (cold). This he did but the pressure rose back up to 2.2 Bar. He has confirmed the filling loop is closed. Any suggestions as to what is going on? Boiler is in cupboard off bathroom and is highest part of the system.

 

[SJB060685]

It's not a combi is it?
Expansion vessel is first check

 

[Clint B]

[Sounds like pressure vessel has either split membrane or pressure is down on air side. Pressure is building up as water heats no expansion so pressure rises and operates pressure relief valve.

 

[Wile.E]

It's not a combi is it?
Expansion vessel is first check

It is a combi and I think you may be right re the pressure vessel, thanks!
[automerge]1580772930[/automerge]

[Sounds like pressure vessel has either split membrane or pressure is down on air side. Pressure is building up as water heats no expansion so pressure rises and operates pressure relief valve.

Thanks Clint, I believe you may well be right, i will have to check for pressure when next down there and take things from there - cheers!

 

[Gasmk1]

If pressure is increasing when boiler off then there are other problems 1) the filling loop is passing so valves need replacing. 2) the plate heat exchanger has failed and water is passing through this will need replacing by a gas safe registered engineer. Or could be as already said a failed expansion vessel.

 

[Wile.E]

If pressure is increasing when boiler off then there are other problems 1) the filling loop is passing so valves need replacing. 2) the plate heat exchanger has failed and water is passing through this will need replacing by a gas safe registered engineer. Or could be as already said a failed expansion vessel.

The pressure only rises to 5 bar when the heating is on and then it vents so I agree with previous comments that the pressure vessel either needs repressurising or the diaphragm is compromised. Thanks for your comments

 

[Gasmk1]

something wrong as it shouldnt get to 5 bar PRV releases at 3 bar

 

[SJB060685]

The pressure only rises to 5 bar when the heating is on and then it vents so I agree with previous comments that the pressure vessel either needs repressurising or the diaphragm is compromised. Thanks for your comments

The pressure relief valves are usually 3 bar, some boilers 2.5. I suspect expansion vessel problem as said above. I asked if it was a combi because it could of been the HPX as someone also suggested above. You said you ruled out filling loop.