Hotpoint 7821 Dishwasher - programmer stops mid cycle?

This has worked fine for years but the last two times I have set the machine on a full wash cycle (No.2), the cycle runs until the programmer knob goes just past the "brush" symbol. The programmer then stops and nothing more happens. The items are washed OK but not properly dried. i.e. no heat cycle.
Is this likely to be the programmer itself, or a sensor failure please?