Worcester 350 pressure problem

[Whaqatac]

I've a Worcester 350 combi boiler and when I have turned the central heating back on last week, the pressure increases to 3 bar as the system heats up but when I turn the wall thermostat off the pressure will drop back to 0.5 bar. I am having to constantly fill the boiler to bring it up to pressure to use just hot water after I have run the central heating.

I've read elsewhere in the forum that the problem could be the expansion vessel (the large red tank on the front of the boiler, I'm assuming!) and when I have checked the valve on that it pours water out.

Should the expansion vessel have any water in it at all?

Thanks for any help anyone can give.

 

[tomy]

If water comes out of the valve on the expansion vessel it is definately knackered.

 

[Whaqatac]

Thanks Tomy,

thats what I guessed, looks like I'll be changing it then!