Ronald0,
Thank you very much for your second response---it's solved the problem.
I followed your first suggestion and went to the pump, only to find it wasn't turned on---the BG man had left it turned off!.
Turned it on and within a few minutes downstairs rads are warming up.
Again...
There was a cylinder stat fitted, set to 55, but the replacement he did to the valve seems to have sorted that problem.
There is a downstairs temperature control on the wall.
Sorry, not sure what you mean by pump speed, or how to speed it up.
Appreciate your help.
BG came yesterday to fix a problem under our service contract.
The water in the hot water tank was scalding hot. They diagnosed it as a faulty valve and fitted 'zone valve,inners,actuator and cylinder stat'. It seems to have sorted the problem.
However, in the evening we found that none of...