I know this is a common issue and I have searched but i haven't found a definitive answer.
Overnight my fans suddenly will only blow cold air.
So far I have removed the heater control valve and tested it and its fine. I've also bled the cooling system to try to remove any air stuck in there. And yes I am sure the setting is on the 2 red dots by the center vents.
I'm thinking now the thermostat or final stage resistor... is there any definitive way to test both of these because I dont like wasting money replacing bits if im not certain it's going to solve the problem, or could it be anything else i haven't thought of?
ADDITIONAL INFO: I am able to control the fan speed as normal, which i have been told means its not the final stage resistor at fault but im not 100% sure on this, anyone?