It's of an age where all the faults mentioned in this thread are possible, plus a few that ain't.
Sometimes on an old system with lots of crud the pipe to the inbuilt expansion tank blocks up and stops the tank working, tank can be fine, on worc the pipe comes out with the tank, pul a sliding clip, remove a screw at the top, pull tank and pipe out.
If in doubt Harry hill is going to be along soon.
Sometimes on an old system with lots of crud the pipe to the inbuilt expansion tank blocks up and stops the tank working, tank can be fine, on worc the pipe comes out with the tank, pul a sliding clip, remove a screw at the top, pull tank and pipe out.
If in doubt Harry hill is going to be along soon.