What the Error Code Means
Error code 31 generally means the furnace detected an airflow or venting condition and paused for safety.
It points to a safety condition rather than a single confirmed failure.
Common Symptoms You May Notice
- The furnace tries to start but shuts off before warming the home.
- The blower may keep running while heat stops.
- You see the 31 code flashing on the control panel or indicator light.
Most Common Causes (From Least to Most Serious)
- Restricted airflow: A dirty filter, blocked vents, or closed registers can reduce airflow and trigger a safety stop.
- Return air is limited: Furniture, rugs, or storage blocking return grilles can make it harder for air to circulate properly.
- Venting is not clearing normally: If outside intake or exhaust areas are blocked by debris or snow, the furnace may shut down as a precaution.
Safe Things You Can Check Yourself
- Turn the thermostat off, wait a minute, and set it back to heat to see if the code clears.
- Replace or clean the furnace filter if it looks dusty or clogged.
- Make sure supply vents and return grilles are open and not blocked by furniture or rugs.
If at any point this feels unsafe or unclear, stop and contact a professional.
When to Stop and Call for Service
- The code returns quickly after a reset or during every heating cycle.
- You smell burning, see smoke, or the system shuts down repeatedly.
- The furnace will not produce heat even after basic airflow checks.
Typical Repair Cost Range
$150-$450 is typical for diagnosis and service to address airflow or venting-related furnace issues, depending on the cause and parts involved.
Costs vary by region, model, and provider. Request an estimate before approving any repair.