what needs replacing?

There will be a heating element - a fan will blow air over the element to make warm air - a thermistor in the airflow will provide heat information to the control board - there may even be a thermal cut out (thermal fuse) as a safety measure against overheat.

The element may be defective
The fan may not be working
The thermistor may be defective
The control; board may be broken
The thermal cut out may have operated

Your appliance engineer will know better than I do and will soon sort you out - my answer here is all guesswork. The most probable cause is likely to be the element.

Good luck...

Peccavi
November 2009