I have inherited a central heating system with 8mm microbore. All radiators in the system get hot except one problematic radiator. I have taken the old radiotor off, flushed it out with a powerwasher which had no effect. I've replaced the old radiator with a new one so I know the radiator is not full of sludge but it's still not getting very warm. When I had the radiator off, I checked the flow in the supply and return pipe, neither were blocked.
I'm left thinking that there may be a partial block in the supply pipe which is reducing the flow and I have therefore added a cleaner to the system in the hope that this might move any blockage, although after nearly a week of running for four hours a day, the radiator is still cool.
Does anyone have any suggestions as to what to try before I resort to re-piping?