The more you catch , the more you maximize your CP , leading to even better finds ! <| sep |> So because some random group says it happened it must be true , right ? It ' s not like the system was built to invalidate such votes , and has been working fine for decades , right ? <| sep |> I find it odd that when your TStat is not calling for heat your furnace sits idle as if everything is normal , but when it is told to heat it goes into this emr . heat mode If it did not turn on the vent motor in this mode I would almost say that the furnace seems to think it has electric strip heat instead of gas . Did you do anything odd before this problem started ? Did you reconfigure the furnace ? Change dip switches ? Add a new thermostat ? Electrical issues in the house ? Install a generator ? Anything ? If you did none of these things and it went from heating fine to this problem then you may have a failed main board , but an experienced tech will be needed to check all the inputs and outputs to confirm .