What this code means
A switch in the main limit circuit remained open long enough for the furnace control to enter limit lockout.
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, avoid repeated reset attempts, and schedule GreenFlow service.
Frequently asked questions
What does 13.1 mean on a Heil N96MSN1002120A*?
A switch in the main limit circuit remained open long enough for the furnace control to enter limit lockout.
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.