I have recently had a problem with my heater in a ford fiesta always blowing hot air. I had a look at the HCV and found that this was broken (plunger had broke inside) and replaced it. This has not fixed the probem as i'm still getting hot air even on cold. I thought it was a faulty HCV so got another one and still have the problem. When the engine is off and the ignition is turned to on (so the engine is not running) it blows cold air on cold but as soon as you turn th engine on the hot air comes out. The thermostat was changed only a couple of months ago. Have had a look at the control knob and no lose wires behind it. At a bit of a loss as to what to do now. Can anyone suggest anything.