Bosch Classix Slimline stuck on pump & filling stage

I have a freestanding Bosch Classix Slimline SRS43C22GB/04 dishwasher that appears to be stuck on the first stage of the cycle.
When I select any of the wash programmes it will drain then fill for about 2 mins (filling drainage well and about 1 cm over the bottom). It will then drain & fill in short repeated cycles & the “Check Water” light comes on (4 one second drain pumps then 10 sec filling) – this process repeats indefinately. The cleaning cycle or heating does come on.

If I select the “Reset 3 sec” option it will drain successfully.

Would be very grateful if anyone can suggest how I might repair it…..