These models have a tendancy to do this. Air flow across the heater element in the heated box is critical. remove the heater box a check that the fan is operating and not come loose or fallen from its drive shaft. Also remove any fluff etc and retest all should now be OK if not you may nee to change both sensors again the sensor at the front is only accessable from the inside so change it when you have the air box removed
Adam Evans, December 2009
