We have a combi boiler - and radiators in every room. One radiator only
is not working. It becomes mildly warm but that is all. I thought the
problem might be the thermostat on the rad, or, less likely perhaps,
that there may be air in the system (the radiator is in the middle
floor of three floors) - Is there a way of checking/ repairing the
thermostat or of bleeding the system?

Regards - Pete S