Heil furnace LED flashes 12 times; blower may run unexpectedly or not at all, and heating cycles may be erratic.
Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
Possible Causes
How to Fix / Troubleshooting
Safety: Turn off power before adjusting blower wiring or speed taps.
Steps to check:
- Wait out calibration: Some Heil ECM blower systems perform a calibration run after power is restored. Allow 10–15 minutes to see if the code clears on its own.
- Check blower wiring: Verify that the blower motor plug is fully seated on the control board and that speed taps (for PSC motors) are connected to the correct HEAT/COOL terminals per the wiring diagram.
- Inspect ECM module: For ECM motors, ensure the low-voltage communication harness is firmly connected and not damaged.
- Power reset: Turn power off for 1 minute, then back on and observe operation.
When to call a pro: If the blower runs continuously or not at all and the 12-flash code persists, a technician should test the blower motor, ECM module, and control board and reconfigure blower speeds as required.