Ariston LI62 – Program light 1 stuck on

Hello,
I hope someone can help with my dishwasher problem. This built-in model has 4 program lights and a power switch. It’s been working fine for the last month (since we moved into the house). When switched on, the first program light is on (solid) and the program button does nothing – no beep, no program change. Closing the door of the dishwasher does not start the program so all in all it seems to be stuck!
I called Ariston and they told me it’s indicative of the float switch in the sump but I’ve looked in the sump cavity and it’s dry.
I’ve also managed to manouver the unit forwards so I can access the buttons with the door closed but the test-mode I read about elsewhere on the forum does not seem to start. (hold ‘P’, on-off-on, press ‘P’ 3 times etc)
So.. is it likely to be a faulty float switch (seems unlikely to me) or a controller or something else?
On a side note, the dishwasher says it’s a LI62 although the ariston website only lists LI620 or LI62UK. Which one would it be if I need to order a replacement control board?

Thanks!