Bosch SMS40T32UK sporadic drain/check water issue

Hi all,

The Check Water light has been coming on after a cycle, before the drying phase. When I open it, there is water standing in base of machine.

I have checked and cleaned the impeller on the drain pump, and the filter is not blocked either. Have checked the outlet hose, which is not kinked or blocked as far as I can tell.

I’ve tried baking soda and vinegar and all that witchcraft.

BUT, if I bale out the water and put it on the Pre-rinse mode, the cycle runs normally AND the drain pump kicks in and drains the machine. Then when I put it on a normal cycle again… Check Water light comes on and standing water again.

So the pipe can’t be blocked, and the pump must work – because I can watch it drain out on the Pre-rinse cycle.

Could this be a sensor issue, or is there a hidden part of the drain/sump I can access to find an intermittent blockage?? I’m happy enough taking it apart if I know where to look!

Any help most gratefully received!!!

Oak