Thermostat not turning off radiators at right temperature

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Hi everyone,

I installed my wired thermostat a week or so ago and all has been fine but all of a sudden, the thermostat is not turning the radiators off at the right temperature.

My smart schedule is set to 19 degrees at this very moment and the thermostat is measuring 21.9 degrees. But all the radiators are on and have been for a while. No matter what temperature I set the thermostat to, it won't turn off the radiators. Why?