Looks Like There Is No Heat

Hello, I have a problem with my 2007 Executive 1.6hdi vehicle, there is no temperature in the vehicle, but as soon as the fan is activated, the temperature gauge reaches the maximum, the temperature screen appears, but after 3-5 seconds it returns to normal. The sensor, the sensor socket and the fan were changed, but the problem did not change. Anyone have an idea about this?

Does it do this the first time you run it? While the engine is cold.

As far as I understand, the temperature sensor socket, the temperature sensor and the fan must have been changed, what's the condition of the thermostat, has it been checked?