Please,
DO NOT use that heater like that and replace that pressure switch
NOW. It doesn't have to be in a RayPak box, any generic will work as RayPak just buys them from TecMark. Between $22-$24 online.
Of all the things someone can do to force a heater to fire, that is the most dangerous. That heater now "thinks" that there is enough water flow for it to safely fire, even with the pump off. You really don't want to see what a runaway heater can do. I've seen it twice and it isn't good. The temperature in the combustion chamber can reach 2000 degrees.
