Replace 3 port valve actuator which has stopped functioning.
Unit moves from 'hot water only' to 'both/heating' but will not move back to 'water only'.
I believe the valve itself is fine as its position can be changed from inside the actuator casing.
Valve is part of a back boiler system in otherwise good order, located under floorboards of on the 1st floor airing cupboard by the pump/hot water tank.
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