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Safety Overflow Switch (SOS) gone bad on Goodman gas furnace

mikesal3731 Member Posts: 4

My furnace was blowing cold air and LED flashing 4 times (Open High Limit). After a lot of switch testing, and duct/filter checking, I noticed the Diversitech SOS condensation monitor on my gas furnace (https://www.diversitech.com/en-US/item/id/2070) had a subtle amber light. It is the type that snaps around the white 1 inch pvc drain pipe. Somehow it can detect a water back up even though it's attached to the outside of the pipe. I found that if I jump around it (thermostat heating wire directly to circuit board) then furnace works normally.

However, if I go back to normal wiring with the SOS on this line, I get 4 flashes (Open High Limit). If I push the "press to test" on the SOS the furnace works fine as well.
So, I'm trying to determine what's going on with this SOS and why it would cause the open limit flashing sequence. I observe no evidence of water back up and I'm hoping I do not need to buy a new SOS, they are about $100.

Any feedback/info on this would be greatly appreciated!



  • Big Ed_4
    Big Ed_4 Member Posts: 2,074
    I would pour water down the drain to check for any blockage .. You may have a bad sensor ..

    What is odd you say that detector is wired on the thermostat circuit which would not trip the open limit on the board.. Hmm Check the limit curcurt , it will be in series . It may be the yellow wires I am thinking .Check the wiring diagram ...
    I have enough experience to know , that I dont know it all
  • Ironman
    Ironman Member Posts: 7,076
    You shouldn't have a drain safety switch in the line from the furnace. What if it shut down the furnace in freezing weather and you were out of town? You'd have a million times more water from a busted pipe than the furnace could ever produce.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
    HVACNUT Member Posts: 4,864
    Get rid of that and install an EZ Trap EZT-626
  • mikesal3731
    mikesal3731 Member Posts: 4
    Thanks for all the tips... I bypassed the safety overflow valve and connected the thermostat line directly to circuit board and everything works fine.