Earlier I posted a help request under the heading 'Digital Thermostat problem'.
The problem ahs now been resolved following the visit of an engineer under my CH insurance scheme. It was nothing to do with the room thermostat but sludge in the boiler. However it seems sludge problems are not covered under these CH insurance schemes and therefore the engineer could do nothing for me. He did however recommend a treatment of 'Sentinel X 300' which I subsequently injected into a radiator having first removed sufficient water to accept a litre of the sludge cleaner. The results were dramatic within hours.
So if you have unsolved CH boiler problems do check to see if you have a sludge problem before replacing expensive boiler parts. One way to tell is to feel both the top and bottom of your rads. Any marked difference in temperature indicates a problem with sludge. My problem was not so much in the radioators but in the boiler causing it to overheat.
