I have a two year old. York heat pump model GFD04821G with a G9YS100C20DH11H gas heat exchanger and York T8411R1443 thermostat that has been acting up the last few days.

The other day I woke up with no heat. I looks like the installer set this system up so it uses the resistive heat coils for Aux heat instead of the more efficient gas heat exchanger, so I set it on emergency heat when the temps fall below 35 to run the gas heat.

On the matter of the current problem, there is no ignition attempt at all and the status LED flashes red 3 times, pauses and repeats. The troubleshooting section of the User's manual is no help, since it simple says call qualified service man with any code other than 2 or 5. I cycle power and all looks good until the induction fan kicks on. It runs a bit, no ignition and error code comes up again.

I checked all of the hoses and induction air inlet and outlet pipes (nothing seemed to be blocked and significant air flow through the induction pipes when the fan is blowing) as well as the electrical connections. I drained condensate from everything and it finally fired up. I figured it was either condensate backup being sensed or a poor electrical connection and went to work. The unit appears to have two air pressure switches on the heat exchanger. Everything was running fine when I went to bed that night.

Wake up and no heat again the next day. This time I just switch the thermostat off "emergency heat" to "heat". System kicks on and eventually inside temp matches the set point and the system shuts off. I move the set point up a notch and go down into the crawlspace to see what things look like. No error indications, but no gas burning. Apparently running on resistive Aux heat. Check the hoses again and go back upstairs and switch to emergency heat. Back down in the crawlspace, it's burning gas with no errors.

Both of these nights, the outside temp dropped into the 20's F. Been a warm winter, so that really hasn't happened before. Both mornings, things started working as they had after futzing for an hour and the temp back up to around 30 degrees, so I'm wondering if the colder inlet air is related.

Any suggestion on what is the most likely cause of this problem?

Check to insure the vent pipe is pitched upwards from furnace to insure condensate does not accumulate in vent pipe, make sure pipes are clear outside and at least 12 inches apart so the combustion air inlet does not suck in the vent exhaust and ice up.