A lot of Fords after 2000 have (in my opinion) needlessly over engineered electronic controlled heater valve & control (rotary dashboard) switch. Either could be faulty. I seem to recall disabling the under bonnet valve as a temporary measure. I think they`re about �60 a piece, check with your dealer. The dash one can be checked with a handheld meter. Oh, yes, it`s a common fault, Google it.