You need to get the circuit checked from the valve to the heater control panel. If this proves ok, then it is likely the heater panel is at fault. Not uncommon on these. Find a good s/hand unit Price new from Ford dealer is a whopping £400.!!

Yes, the mechanic suggested it must be electrical. Guess I'll have to save up to get it looked at! Thanks for your response.

You need to get the circuit checked from the valve to the heater control panel. If this proves ok, then it is likely the heater panel is at fault. Not uncommon on these. Find a good s/hand unit Price new from Ford dealer is a whopping £400.!!

My Puma started blowing only cold air in the middle of winter, valve diagnosed as the culprit, dealer sorted for £100 all in.

3 years later in the middle of summer it started blowing hot air only. To stop me baking I simply clamped one of the hoses to the valve with the hope that come winter I could cope with heat all the time. Sold the car making the buyers aware that it could be either the valve or panel. They clearly hoped it was the valve and took a punt, never heard from them so no idea. As said above the panel is V Expensive.

Presuming you haven't left the temperature setting high then it must be a hot/cold air flap control issue

These cars do not have a flap (unless they are the poverty model?), the temp is controlled by the electric valve in the water pipe on most versions. When you cannot change the temp its either the valve or the control panel.

I've changed dozens of these valves, its possible that it was not fitted correctly, the temp control should be set at the midway (warm position) before switch on and start up if not it can jam, they are also so poor i've had proper ford ones fail the day after fittting.