It isn’t simple. But you might have expected that it wouldn’t be.
Highest probability is that it’s the flow meter in the fill chamber that’s kaput if I’m right which is, this one. I cannot guarantee that that that cure it of course but, I’d be pretty confident that it would.
I thought it was f6 to start with but the led also flashes 12 times rather than 6 which is why I think it’s fb. Water does flow but after 2-3 minutes it stops and the error code pops up. :-/