Raypak Unitherm Governor Plug blew out today - why?


New member
Oct 30, 2016
Elgin, IL
Unitherm Governor Plug blew out today, I was not around when in occurred. I tested the Unitherm Governor (UG) in a pan of hot water, it cycled open and appeared to function properly. What else could cause the plug to blow?

I am debating purchasing a complete header kit, but what to make sure I am addressing the root cause.

Of note, I replaced the heat exchanger this summer, my old one had a small leak that corroded the lower studs and heater frame. I found an old unit in good shape to fix the frame and bought a new Hx. Everything appeared to work properly with no leaks up to this point.

Pool Clown

In The Industry
Sep 5, 2008
Silicon Valley, CA
I get those once in a while. Its the plug that shrinks a little. May be a use issue, or a material (part) issue. I have never really investigated it since the plug is easy enough to replace, and that seems to resolve the issue. Either way, i remind the owner to let the filter pump run for about 5 min after the heater turns off to let the water draw the remaining heat out of the heater , especially if you are heating the hot tub. If you turn the pump off while the heater is heating the hot tub, The water inside the heater can get pretty hot. I believe this is what shrinks the plug (my opinion).