Temperature Guage permanently on max

I have a Diesel 1.4HD1 8v C3. It has done 130K miles and I love it to bits. The temperature light has been going on and off for a while & my mechanic can't find anything wrong. On Friday the temperature guage came on during my 15 mile drive home & stayed on. It was still on yesterday when I did a 2 mile trip and the fan was still going 10 minutes after I switched off the ignition.

Today I took all the existing liquid out of the coolant resoviour & replaced it with new coolant, to a level inbetween the min & max level. I've taken the car for a test drive & the temperature light is still on max.

Is there anything else I can try before I have to take it to a main dealer for a diagnostic check?

Thanks

The editor wrote:I've taken the car for a test drive & the temperature light is still on max.

It could be a bad temperature sensor or a problem with the wiring from the sensor to the engine ECU.

The editor wrote:Is there anything else I can try before I have to take it to a main dealer for a diagnostic check?

Change the sensor, inspect and test the wiring and connect the car to a Lexia system to read live data and engine codes.

Lexia help: https://citroenc3owners.com/citroen-c3-t ... -t655.html