Washing Machine only works at 30 degree setting?

I have a problem with a Bosch washing machine ENR WFF 2001 GB/01, FD 7804 00834.
The machine fills, operates the drum and the heater comes on if the setting is 30 degrees; above 30 degrees it does not start. Other functions such as pumping out are OK. The temperature probe is 5.23 K Ohm at room temperature.

When I replace the probe with a, possibly non-Bosch, alternative with resistance 26.3 K Ohm the machine fills and operates the drum at all temperature settings; the heater comes on at all settings but only for a few seconds. Exactly the same symptoms result from an open circuit probe!

Thanks in anticipation.

Alan M