from what I can see in the tech the on off sw does not stop the live going to the pump so the overflow switch can work
I would
switch machine on and confirm the pump is still running with switch in the off position
pull out the plug and remove at least one wire from the overflow switch then plug unit back in to see if pump is still running
if no you have found it if yes remove the board. pump seem to connect between connectors B1 and B2. B2 is permanent live so should buzz through to lice connection to board. Now trace b1 until you find the pump triac and check it for short cicuit. remember to reverse you meter leds and check it both ways if you get no reading as triacs can become diodes and feed halve wave to the pump and it would still run
Dave