How to stop pump running - NO water in system?

I have an AEG Favorit - F34300VI0 where the pump is operating continuously. 3 beeps error Code 30 I believe. I've seen a lot of suggestions of tipping the machine every which way to resolve the issue but have had no luck trying this. I've gone as far as completely removing the entire hydraulic system (sump/cassette/water softener/ Integral motor/pump) and emptied all the contents into the sink so there is categorically no water left in the system. Having reassembled the lot and hooked back up the problem still persists. The only thing I didn't do was separate the motor from the pump itself as these are connected via numerous clips, but the impeller spins freely and I couldn't detect any blockages in the pump.

If anyone can suggest a reason this continues I'd be massively grateful. No issue with replacing the parts, just need to identify what's at fault first. Possibly defective Float switch? It would be handy to know if there is more than one of these as the obvious switch is located at the very base of the machine with a styrene float attached. I've detected absolutely no leaks.