Vaillant boiler overpressure mainly when in use?

[lisamj]

Hi all,

We had some troubles with our microbore system / Ecotec Plus 831 Boiler. To cut a long story short, Rads weren't all getting hot, so after a chemical flush, power flush, & 2 new PCB'S, the system was working again. Engineer said to keep an eye on the pressure as it was quite high, and could be the isolation valve.

We've kept an eye over the last few days and pressure keeps going up to 3 or 4 bar. Its mainly ncreases when the heating is on/hot water is used. We have to keep draining some water out of the boiler to get the pressure back down. Have bled all the radiators and theres no air.

Can anyone give us their thoughts on what else the problem could be and if there's anything we can do ourselves? Reluctant to pay another £55 call out if it is something simpler!

Thanks

 

[GavThePlumber]

Expansion vessel faulty

 

[lisamj]

Thanks Gav..... is that your 'diagnosis' from my description, or just another possibility other than the isolation valve?

Thanks again

 

[GavThePlumber]

Could be the filling loop, but that should have been detached.

Edit: On checking the flow iso valve has the fill tap connected to, so if this is the problem, you need to drain the system to change it.

It is difficult to identify problems over the internet, as i am sure you are aware and this is only my opinion.

 

[picasso]

I would check the filling loop first, it sounds like its passing, failing that a pinholed plate heat exchanger would be the next suspect.