My 1.3 2008 Mazda 2 has been over heating. It did the first time on a the way back from a weekend break. It was fine going there, but on the way back it started to over heat after about 40 miles.

Ive had the thermostat changed the engine coolant sensor changed. Fresh coolant, cleaned the bugs out of the radiator and pressure tested and it was fine? Blocked radiator? The cooling fan kicks in around 100°c
If I turn on the heater on in the car it cools down

 

. Does the heater stop the overheating or is the heater starting to blow cold? If second option then could be water pump.

 

Yes the overheating stops as soon as I put the heater on in the car. It blow hot air out

 

So its less likely to be the pump. Another thread suggested a mazda dealer to check ecu , thik te said they could do a diagnostic cheeck