Boiler loses pressure suddenly and cuts out when heating has been on

[Giles Mann]

We have an Ideal Independent C24 boiler.
Since we moved in just under a year ago we have had to re-pressurise a couple of times using the filling loop; which I have read is fairly normal.

The other day I needed to re-pressurise again. I may however have accidentally left the filling loop valve slightly open as, it was about 2.8 bar when I looked at the gauge a little while later. I bled a radiator to reduce back to just over 1 bar and everything seemed ok.

Since this, every time the heating has been on for a couple of hours or so, the pressure suddenly drops causing the boiler to cut out.
Would this seem to suggest an expansion vessel/PRV issue rather than a leak in the system?

Cheers

 

[Giles Mann]

Update - since last night when I re-pressurised to just over 1 bar:
Today
- 4pm The pressure had risen to 1.5bar (only use since was a shower in the morning)
- 5pm was fine with my partner having a shower pressure went up a bit to nearly 2 bar but came down again after
- 6pm heating came on - after about 30 mins the pressure was nearly 3 bar. We turned the heating off and the pressure started to reduce
- 7pm went to check the gauge and it was down at 0.5 bar (boiler wouldn't fire when tried)
- I have since re-pressurised again but for the time being I am only going to use hot water and not heating

 

[terryplumb]

Sounds like the EV isn't functioning ,may just need to be re charged. And the PRV may need attention if it doesn't close fully .