Erratic boiler pressure

[Katethemate]

I wonder if someone could help. Our boiler is acting strangely. It's a five year old Vokera Linea 735.

The boiler was re-pressurised and radiators were bled, including one radiator on the second floor. It was re-pressurised to 1.2 bar.

When the heating switched on the pressure rose to 3 bar resulting in water expelling from the system.

While the heating was running it seemed to stabilise round about 1.5 bar.

Then we ran a shower for about 5-10 mins and the pressure slowly dropped to around zero. When the shower stopped running the pressure stayed at around zero until repressurised.

Can anyone tell me what's going on with the system? Is there a possible leak in the switching valve which switches the external heating loop on and off or is it possible there's a problem with the pressure meter?

Any information gratefully received.

Cheers.

Kate the Mate's husband (she's no good with plumbing!)

 

[electronicsuk]

Sounds like the expansion vessel needs recharging to the correct pressure, or the diaphragm inside said vessel has ruptured which, realistically, will mean replacement.

If you found the radiators to contain a lot of air when bleeding, it's possible this problem has existed for a while, but the air gap in the rads was taking up the increase in water volume as the system heats up. With that expansion space now gone, the extra water has nowhere to go but vent through the PRV.

 

[Katethemate]

Sounds like we need to get a heating engineer to put it right. There was quite a bit of air in the radiator on the second floor and after bleeding a lot of water did leave via the PRV. After we ran the shower, I re-charged the pressure back to 1 bar and when the heating switched back on a lot of that extra water seems to have been expelled through the PRV.

What you're saying seems to make sense, electronicsuk, at the moment the heating is running on 2 bar.

I suspect running the hot water again may result in the pressure dropping to zero again.