Can anyone help me solve the mystery of why the heater on my son's Ford Fiesta (Mk 6?) 2012 is not blowing hot air, only cold? All four speeds on the fan are working, the drivers side control arm/lever from the rotary heater temperature dial seems to be connected and operating correctly, I've flushed through the cooling system with Holts Radflush, connected garden hose to the bulkhead inlet and outlet pipes and seen apparent flow through the matrix both ways, and checked that both inlet and outlet hoses are hot with engine up to temperature. The only 'easy' thing i have left to check are fuses and of course, I want to do all i can to avoid having to remove the whole fascia to get at the heater module. Any suggestions?  

Edited August 24, 2025Aug 24 by TheVallog
Factual error

31 minutes ago, TheVallog said:

Ford Fiesta (Mk 6?) 2012 is not blowing hot air, only cold?

Possibly because the car is having an identity crisis? 🤣

2012 = Mk7 in the UK

The heater air blend door is stuck inside of the heater box. If you are lucky it might be able to be freed by moving the arm on the side of heater box.

Thanks. The side arm seems to move freely up and down already, actuated by the cam operated by the rotary dashboard control. Are you saying that the arm may not be moving the door itself? 

21 hours ago, unofix said:

Possibly because the car is having an identity crisis? 🤣

2012 = Mk7 in the UK

Yes, I appreciate that now. This was why I added the question mark. 

2 minutes ago, TheVallog said:

Are you saying that the arm may not be moving the door itself? 

That could be a possibility.

The heater core on your vehicle always has hot water flowing through it regardless of the temperature setting.

Selecting the air temp is simply achieved by blending cold air from outside with warm air that is passed over the hot heater matrix.

1 minute ago, unofix said:

That could be a possibility.

The heater core on your vehicle always has hot water flowing through it regardless of the temperature setting.

Selecting the air temp is simply achieved by blending cold air from outside with warm air that is passed over the hot heater matrix.

OK, so the good news is tha the matrix is unlikely to need replacing. The bad news (presumably) is that there's no way to free a stuck blender control flap other than by (a) jiggling the arm and trusting to luck or (b) taking the whole thing apart with all that entails. Don't suppose there's any way of jarring it open or applying lubricant?  

I'd be concerned that the arm is free to move but the blend door seems stuck. That would possibly mean that something has become disconnected inside the heater box.

If the heater box has to be worked on then that will mean the whole dashboard will have to be removed, a major job !

2 minutes ago, unofix said:

If the heater box has to be worked on then that will mean the whole dashboard will have to be removed, a major job !

Well, you're not wrong there. Horrific...