Conventional pumped, open, CH system that has worked well for a number of years. Inhibitor changed every couple of years etc, system generally looked after.
Recently, it has got very noisy "clicking pipes", esp. in the morning, "rattling" in the pipes and some cold radiators (but not in an obvious pattern, rads that are close, physically and pipe wise, one is hot, one cold). Some downstairs rads are cold, some middle floor, all upstairs fine.
System has been checked for "air" and it has been balanced OK in the past.
Pump seems to be running fine.
I've not checked the header tank (getting to it isn't easy at the moment- I've just got of of hospital) but there seems to be water in all the rads.
Any ideas?
Brian