Bosch Dishwasher E09 error code - help please!!!!

[Woodfortrees]

We have a Bosch Dishwasher (SMS25AW00G/56, Serie 2 SilencePlus). Says error code 09, which apparently can be caused by a failed heating element, a faulty control board, or an incorrectly functioning sensor that doesn't detect water & salt levels properly.
So I've read that we should check the salt sensors.
What other things can we do you check this out please?

 

[Woodfortrees]

I spoke too soon - how do we even find the salt sensor?! We've got the heat pump out, but I can't find any video tutorials on how to find the salt sensor...