Ahh. Differences in terminology then. I meant if a smart TRV was in a different room to the roomstat, could the smart TRV still get the boiler to fire even if the roomstat was satisfied. EG roomstat is in hall. Hall has reached set temperature but a room with a Smart TRV is below set temperature. Can the smart TRV still get the boiler to fire even though the roomstat in the hall has already turned off the boiler?Your question was "can the Smart TRV's override the thermostat and turn on the heating by themselves?".
If the roomstat & smart TRV are in the same room then "no" is the correct answer. If they are in different rooms, the TRV is not overriding the thermostat as they control separate areas and either can independently turn on the heating.