Hi guys,

I've just taken a 57 Plate Zetec S as PX and it keeps boiling up on me. It drives fine for 10mins or so, temp gauge doesn't even go up halfway, but then it will boil up whilst driving. When it gets hot the radiator and the rad pipes don't feel hot, whereas the heater pipes are hot to the touch. Also the rad fan doesn't come on, presumably because the temp switch isn't getting hot. If you disconnect the sensor the fan does come on, so I know that it works.

So far, I've changed:

Thermostat
Temp sensor
Waterpump (although on inspection the old one looked OK)

I've just tried some rad flush in it as well, but that hasn't made any difference.

I'm at a bit of a loss of what to try next. Any suggestions?