When unpowered, the motorised valve is held by a spring to close the central heating outlet.
When central heating is required, the motorised valve receives power (on its white wire) from the room thermostat via the programmer to operate the motorised valve motor and open the heating outlet.
If the thermostat, or programmer go 'off', the live should be lost and the spring pulls the valve back to close off the heating port.
It's possible, if it's been wired in wrongly that there is still a live on the white wire when there shouldn't be. Someone with electrical knowledge and a multimeter would be able to physically check this.
I would be grateful for an explanation as to what is incorrect in the above please.