"Christian McArdle" wrote in message
...
Is this a major problem with the central heating system or one
that I can easily repair?

It is a major problem. Water is clearly getting into the system. You need
to
identify where. Some possibilities.

(a) DHW heat exchanger in a combi boiler.
(b) Leaking indirect coil in an unvented hot water cylinder.
(c) Filling loop not disconnected after filling.

Basically, anywhere mains pressure water comes into contact with the
heating
primary circuit is suspect. Depending on what the final diagnosis is,
fixing
it could be cheap and easy, or very expensive.

Christian.




Sounds more like the expansion vessel has lost it's air volume.

It could be that the diaphragm has burst, and the thing is full of water,
or it may just need re-charging via the schrader valve.

Read he
http://www.makewrite.demon.co.uk/SealedCH.html
Scroll down to the section:
I suspect the expansion vessel is faulty, how do I check?

--
Ron