Just replaced mine. Buy a new mono insert. Take out the old one. It's just to the right of the battery. You'll see a two inch square plate with the insert, approx 1/2 inch round, sticking out throught a hole in the plate. The plate is held on by four blade screws. unscrew the plate, unplug the wire, and pull the valve out. The old insert will be surrounded by a copper wound element. Tap out the old insert, slide in the new one, rescrew and replug and you're all set. takes 10 minutes