Samsung Eco-Bubble combi, needs a new drain pump, but there's 2!

Hi, I've become a home grown expert in the terrible joy of maintaining a Combi machine. Samsung Eco Bubble 8kg model. (WD80J6400AW)

I frequently get the 5c error code, so I drain it and I take it apart and clean all the hoses and it normally works again. This time it didn't work so I guessed that the drain pump had finally given up.

I referred to many videos as i haven't done this in many years. I cannot find any specific info for my model, or good info on combi's at all.

But when I took the unit apart there's 2 pumps (DC31-00181A). I started a spin cycle and I could see that one pump worked. I swapped them over and sure enough neither worked, so that looks to me like one is dead. But then the functioning one doesn't work when plugged into the location of the burnt out pump.

So really what I need help figuring out is, is the second pump supposed to work at the same time as the first or does it operate on a different schedule. I've ordered a replacement pump, but is there another problem that I will have to deal with? Could the wires of been damaged, I cannot see any obvious external damage.

I put a volt meter to the wires, whilst on the spin cycle, !st location reads 1v, the 2nd fluctuates between -0.1 and 0.1. Exactly the same readings come out of the plug that the pump wires plug into.

I would appreciate any expansion to my knowledge as I feel I'm basically a washer/dryer combi technician in training.

Thanks in advance