Advice on a F03 thermister fault in an Indesit WD12 washer dryer?

My Indedit WD12 washer dryer is showing a F03 thermister fault (light flashing 3 times, pause, then flashing 3 times). The programme knob is clicking round and the water is both coming in and being pumped out at the same time.

I gather the themister is either in or near the heating element - any advice on testing/changing it please? Or any other thoughts on this fault?