I don't know if Peter Earles does powerflushing but he'd probably be able to point you in the right direction. Powerflushing cleans the entire radiator system, and takes a day. If the thermostatic valves on the rads are getting a bit old, it would be a good idea to replace with new prior to flushing or, at least, replace the valve on the rad that is not working, as there may well be a failure here, which may still hold gunge after flushing if not replaced, plus the rad may still not work after flushing if there is a problem with, or around, the valve. None of this comes cheap.
Michael Brown ● 1291d