Oh yeh, good point. So if the valve has failed then it's failed open and is allowing the water to circulate fully through the heater and therefore i should be getting constant hot air rather than constant cold air?

So i can probably eliminate that as the fault then? Some cars have mechanical flaps in the heater system which direct the air intake through or away from the matrix dont they. I can imagine if the flap got stuck it may cause this issue but I presume this Ford system doesn't have these as the temperature is controlled by this valve thingy.

BTW, i've tried unplugging the loom to the valve to see if it makes a difference... it didnt.

Another thing i thought of was a blockage or airlock in the matrix but yet again, both pipes wouldn't be hot if that was the case i reckon.

The heater valve is quite a pricey item and i can imagine it still being fairly pricey from scrap yards (if i could be lucky enough to find one that works).

Is it possible to test the heater control panel easily enough, anyone know if that's likely to be the problem? Am i missing something else?