Worcester Greenstar 35cdi Pressure Fault

[elnenio]

Hi All
My 4 year old boiler has started loosing pressure, i have isolated the boiler from the system for 48 hours with the heating off without any pressure loss at all, it seems to only be happening while the heating is on.
any ideas as to what parts may be at fault and rough cost of repair, starting to worry xmas may need to be cancelled this year !

 

[Rob]

Whats the pressure guage on cold and what does it get to hot.

9 times out of 10 the leak will either be the PRV, evident by a dripping pipe outside, or from radiator valves.

Check them all aswell as the pressure guage- It should read 1 bar cold no more than 2 when hot.

 

[elnenio]

Thanks for the quick reply,
its 1 bar cold rising to 1.5 bar hot there is no leaks on any of the rad valves hot or cold they have all been double checked and the exit pipe from the prv is also dry, the system had switched itself off this morning and the pressure had dropped to 0, i filled it to 1 bar and went off to work leaving the heating on just checked it again now and it is just above 1bar

 

[bengasman]

Checking prv outlet will do little good. You need to stick a sandwich bag around it and hold it in place with a rubber band.
Just leave it there.
How long between filling up and loosing pressure?
If you fill it up when the system is fully warm, you can safely go to 2 bar or even a bit more.

 

[elnenio]

I will try the sandwich bag although i'm pretty sure the pressure loss is not the prv. is there a way to check if the expansion vessel is at fault ?
thanks for the reply