Indesit DE43 not heating water properly?

My Indesit DE43 dishwasher only heats luke-warm, if it gets through the cycle. It sometimes displays fault code A03 - thermistor short-circuit - and does the drain + 1 minute thing. I cannot find a replacement thermistor on the web, and Indesit Spares themselves say they don't have any such part listed for my machine. Am now at a loss - does the machine have a thermistor? If so, where is it located? (it's not integral with the tube heater - have already bought one, but the old one measures identical to the new one). Can anyone help on this?

Thanks,

Mitch Smith