One room overheating

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One of my 7 room stats is still heating to 24 - despite me switching it "Off" on the App. The underfloor heating actuator for that room is showing that it is drawing heat from the boiler (top popped up). All the other rooms are behaving normally (set at 20 degrees - as set in the Smart Schedule. ) I have tried re-pairing the stat to no avail. Is this likely to be an actuator problem? Thanks for any help.