Good thought Vinny, I missed that.
Pologuy, let's call the flow switch a "sail switch". The thin metal part has a rubber tip that is pushed toward and in contact with the center post of the switch making a magnetic connection recognized by the circuit board.
Rookie mistakes to look for, the metal pins going into the loom have a fish hook that holds them in. If they are flat, they can be pushed back and not make contact with the circuit board pins. However, this would give you a "solid" flow and no other function would work. Not likely your problem.
If that sail switch is not closing, THAT is your problem. That leads back to the movement of water. It is very unlikely, but possible, that you could have an internal blockage in the closed plumbing system.
There is no power to the switch; it is only a switch that closes the circuit that allows the heater to energize.
If you circ pump is hot from running or operating and you do not see water closing the sail switch the circ pump either has debris in the impeller which is driven by a magnetic field and unable to work properly, or the circ pump is not functioning properly and should be replaced.
