Radiator problem

[Clematis]

1980s central heating system so no thermostats on radiators. With boiler (Stanley cooker) on and circulating pump heating up 3/4 radiators closeby (bungalow) another radiator which is sometimes used, warms up even though it is turned off. I've replaced the turning cap as the old one was worn but even leaving cap off and using pliers to turn radiator off there is no difference. Could 'lockshield' valve be a problem? Any suggestions grateful.

 

[Buddyboy]

It is possible that some water is getting past the valves, depending on the power of the circulating pump, and the state of the valves.
Also, there will always be some convected heat as the rad is on a circuit that has hot water flowing past it. It will depend on the length of pipe that goes from the circulating ring of hot water and the radiator. if it is short, then it is possible for the radiator to heat up.
You have to ask yourself, if it is enough of a problem to warrant the hassle of replacing the valves (draining down the system etc.). If the other radiators have enough heat, then maybe it's not.

 

[Clematis]

Many thanks. Was talking to my usual plumber who simply said there could be dirt blockage causing this. Anyway problem has now resolved itself so happy days!