I have a Warmflow Central Heating Boiler (about 25 years old) which does not switch off when it has reached the set temperature, but continues to run till the radiators are extremely hot. It then switches off. Is this a thermostat problem and is the cure straightforward if this is the problem. I know I'll probably be told that age is the problem but this is a boiler which is lightly used and has never given trouble before, so I'm hoping that the condition is not terminal!
Yes .. bound to be the thermostat/control/sensor. I suppose you could remove the assembly and test it. Parts ought to be available. You can find on web.