we answered our own question! Their are two chambers at the back of the water tray - the magnet goes at the bottom of the chamber that has plastic housing half way down it. This allows the float to fall as the water nears empty.
despite this we still kept getting the water empty warning, since the magnet in the tray wasn't strong enough to trigger the reed switch behind the panel of the coffee machine. So we stuck a magnet onto the back of the coffee machine aligned to where the magnet in the tray would be when full. Remember magnets have dual polarity so if doesnt work turn it over (you want to replicate the polarity action of the magnet in the tray)
david, July 2021
