Excess pressure in sealed CH system

[JonS]

After replacing a TRV on a radiator recently the normal running pressure of my sealed system has increased from approx 1.75bar to just under the pressure release value of 3 bar. In fact, the pressure exceeds 3 bar slightly and water is lost and the cool system pressure is then sits at just under 1 bar.

I have thoroughly bled the system. The oil-fired boiler is not overheating and cuts in and out as normal.

Does anyone know why this change should have taken place? Is it anything to do with the expansion vessel?

Thanks for any feedback

 

[Slugbabydotcom]

Sounds like a pressure vessel to me. Just make sure your filling loop is disconnected to eliminate the possibilty of Fill loop valve not shutting off properly. You can save money by connecting another pressure vessel into the system and leaving the old one where it is.
Sometimes you can get away with pumping up the vessel again. It has a Schrader valve on it and a car tyre pump fits it. Let some water out before you do it and do it when the system is cold

 

[JonS]

Thanks for the reply.

Yes, it was the vessel. It was still under guarantee so a new one was fitted, solving the problem. The faulty one was absolutely full of water indicating a leaking bladder.