What this code means
The furnace control detected a heating demand at power-up.
Safe checks
- Confirm the thermostat is on, set correctly, and calling for heating or cooling.
- Check the air filter and visible return-air path for obvious airflow restrictions.
- Record the displayed code or flash sequence before scheduling service.
First step
Record the code, check the thermostat and filter, and schedule service if the condition remains.
Frequently asked questions
What does 12.1 mean on a Day & Night N96MSN0601716A*?
The furnace control detected a heating demand at power-up.
What should I safely check before scheduling service?
Use only the visible, non-invasive checks listed on this page. Do not open equipment panels.
When should GreenFlow handle this code?
Call GreenFlow if the code repeats, the equipment is locked out, heating or cooling is not restored, or the condition involves gas, ignition, pressure, wiring, a motor, or a control board.