Bosch SRS43C12GB/21 drain pump activating

My parent’s dishwasher stopped working suddenly – would not fill with water, just a whirring noise, whether the door was open or not. Would drain water if thrown in manually. I was not familiar at all with dishwashers before today so bear with me.

It seemed at first like the anti-flood mechanism was activated, causing the drain pump to kick in. I pulled the side off to find it wasn’t activated, and no signs of water in base. Can’t see properly into the main float due to this red cover that doesn’t seem to be present in any guides I’ve found, so not sure if it is blocked or not.

After pressing the actuator manually a few times – to no initial response – a minute later it suddenly kicked in and now appears to be working properly again. I don’t trust it – is it possible the drain pump actuator switch is faulty, or is something else going on?

EDIT – spoke too soon, end of 2nd cycle and the same thing’s happened again.

EDIT 2 – left it for a while and it’s working again. Thrown a load of bicard/vinegar in in the hope it will unblock something if it’s blocked.