There are three temp sensors.
One for the temp gauge, down the back of the engine just above alternator.
One for the cooling fan, in radiator
One for the ECU in the inlet manifold.
The temp gauge one is either working or not, so if you have no delfection it might be the switch (more likely the connection). If there is any deflection its usually telling the truth so your thermostat is jammed open.
Cheers
D