MGF heater suddenly blowing cold

Hi all, my girlfriend's 2001 MGF has developed an issue of the heater only blowing cold air, and I can't figure out the cause. As long as she has had the car, it's been the case that the heater will only blow hot when the knob is turned up to the max, but it has always worked. When turning the knob, you don't get any resistance until it is nearly all the way to max, then you get a small amount of resistance that changes the air from cold to hot.



About 2 weeks ago, I was driving it and switched the heater from hot to cold. When then switching it back to hot, the temperature didn't change and the air continued to blow cold. There is now no resistance at all when turning the temperature knob between cold and hot.



The car has continued to drive with no problems, coolant temp gauge remains normal, coolant usage is normal and oil is fine. I did a 2.5 hour drive yesterday with no issues, other than a lack of hot air! I have removed the heating knob and can see that the spindle continues to turn between hot and cold.



Any ideas as to what may have caused the sudden lack of hot air? I have done a search of the forum, but have not been able to find anything relevant other than the recommendation to check the cables to the left of the clutch pedal, which I will do.

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