On 10 Feb, 13:58, "
wrote:
hi there
I have a pressure prob with a sealed gfch system.

The pressure shoots up and down - according to the FAQ, this prob
means that the expansion chamber has failed, but when I check the
chamber, there is no water coming out of the valve - only air. Air
pressure is approx 10/11 PSI. I keep topping up water, but there is no
apparent leak...

Any ideas?

Blocked connection pipe between the expansion vessel and the system.
Ideal Classic combis were a bugger for blocking where the connection
flex tees off the boiler internal pipes. Many others with small bore
connections blocked within the small bore section.
HTH

John