In an earlier contribution to this discussion,
Sparks wrote:


If the pump is running, turn off the rads upstairs, all but one
downstairs - does this cause the downstairs rad to heat up?


As others have said, you may be able to clear the airlocks in the downstairs
rads by applying *all* the urge to one rad at a time - by turning all the
others off. If that doesn't work, try this:

On each cold rad, turn off one valve. Open the bleed screw and bleed off a
couple of litres of water (into a suitable container!). Then close that
valve and open the other one, and repeat the bleeding operation. That will
ensure that the flow and return pipes are *both* full of water. [If you
bleed with both valves open, the water only needs *one* path - and there can
still be an airlock.] If your system has inhibitor in it, pour the 2 litres
back into the F&E tank after each operation to avoid wasting it.

One other thing to check: I think you mentioned earlier that the rads are
fitted with TRVs. Remove the thermostatic heads and make sure that the pins
move up and down smoothly, and are not stuck down.
--
Cheers,
Roger
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