Baxi 33HE Combi Pressure too high!!

[casey75]

HELP!! Had an engineer out who has done the following to try to fix this problem;
Recharged original expansion vessel to 1.0 bar which didn't work.
Replaced expansion vessel with new and charged at 1.0 bar, which didn't work.
Replaced pressure relief valve, which didn't work.
Checked pipes for blockages.
Gauge seems to be working ok.
Each time pressurised the system whilst cold to 1.0 bar, then turned on heating full which then took gauge up to 2.0 bar. Then overnight the pressure builds up to 3 bar without the heating on!!
All this started from a leaking rad valve that was changed?!

Engineer spoke to colleagues and they don't know either, any help here is much appreciated!

 

[gigz]

Charge to 1bar when cold. Depending on how big the system is, rising to 2 bar is not a problem. Make sure your filling loop is disconnected. If after all this it still rises (especially overnight with heating off) your plate heat exchanger will be passing, and will need renewing.

Edit. I'm assuming its a combi. Did he check the pipe that the expansion vessel connects to the system wasn't blocked ?

 

[casey75]

Charge to 1bar when cold. Depending on how big the system is, rising to 2 bar is not a problem. Make sure your filling loop is disconnected. If after all this it still rises (especially overnight with heating off) your plate heat exchanger will be passing, and will need renewing.

Edit. I'm assuming its a combi. Did he check the pipe that the expansion vessel connects to the system wasn't blocked ?

Yes it is combi.
It definitely seems the pressure rises quicker once the boiler is off.
Checked the filling loop first, definitely not letting by, will suggest heat plate exchanger, thanks for your help.