It still sounds as if there is a blockage on the flow side of the CH
circuit. Are the downstairs rads ok? When you flush the pipes out with an
upstairs rad removed by opening each valve in turn (with the pump off, of
course) do you get a good flow from *both* valves?


Downstairs rads are fine, never need bleeding, and kicking out plenty of
heat. I'll have to get back to you on the flow from both valves
question....all rads are back in place for the moment.


Are the HW and CH circuits separate, or do they share any pipework?

As far as I can tell, they are separate. There are four pipes coming out
of the side of the chimney breast running to upstairs (HW F/R & CH
F/R???). I only know that all pipes come out of one side of the chimney
breast, not sure how they are configured at the boiler itself.


Is this a recent problem, or has it *never* worked properly?

The upstairs rads have always needed bleeding very regularly, and have
always been quite noisy. It's only recently (12-18mnths) that they
appear to empty with the pump running.

Again, thanks for the assistance. It's much appreciated.
Bob