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.