Brrrrrr! No heating!

[CellophaneFlower]

I have a boiler issue. It's a system boiler. Hot water working perfectly but there's a problem with the central heating. I've done some investigating and have found the following: Heating comes on fine, all rads heat as normal, but then pressure steadily rises, until boiler cuts out as obviously it's too high.

I'm thinking either the expansion vessel needs to be recharged/replaced, however I just wondered if there's anything I can try first before I freeze to death get an engineer in?

We had this problem few days ago and my husband bled the radiators to clear some ‘air block’ it is working fine now
worth a try?

Thank you! I was hoping somebody would say this but didn't want to try in case it wouldn't help! I bled one, as before I realised the issue, I topped the boiler up, then released some water when pressure started rising. There wasn't any air in that one but shall try others!

What you describe sounds exactly like the expansion vessel has lost its charge or that the diaphragm within the vessel has perished.

However, the pressure should only rise to just over 3 bar before the pressure relief valve lifts and discharges the excess water outside. When the system cools down the pressure displayed on the gauge should be much less than before it started heating up and will need the water pressure topping up.

Thank you. Yes, this is exactly what's been happening, although since realising, I've monitored and manually turned heating off when it rises to 3, to prevent damage. Then the pressure reduces to normal. Previously it was going above 3, cutting out and releasing all the pressure itself, resulting in me needing to top it up.

There wasn't any air in rads, so have somebody coming to fix.... hopefully quickly!