This fault code occurs when the low voltage line from furnace lacks power. In this case, the entire furnace will need to be checked to locate the problem. This is not usually due to a thermostat failure. In case whereby there is a thermostat issue, one should be very careful when replacing the thermostat. The system uses a so called “communicating” thermostat, which has a very complicated structure and should be examined and, if necessary, repaired, by a trained technician.
This happens due to a low-temperature lockout. You need to reset your system. Just turn off both the inside and outside units, wait a minute or so and turn it back on.
The 126 error indicates poor communication between the thermostat an the furnace/AC unit. Try switching off the furnace and the AC, then switch them on and check the communication. If the problem persists, contact your technical service provider.
If you see the 26 fault code on the display, your unit is overheating. The error appears when the furnace exceeds the set temp limit.
Most likely, it is because of a dirty filter, blocked fan, dirty ac coil and/or blocked air duct.
The 79 fault code means that the low pressure switch is released. This happens when the evaporator coil gets iced up, air filter gets dirty, the system runs low on refrigerant, or when there is a problem in the printed circuit board.