My radiators will not go off?

My potterton kingfisher mf100 will not turn off, even though the programmer is in the off position for both water and heat but the radiators will not turn off. The only way I can turn the boiler off is to turn the switch off on the boiler. What can be done to cure this problem.
Jimbo, April 2018


done
ch motorised valve might be stuck in demand position

?, May 2018
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