Hello,
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!
Mike
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