What This Error Means

A three-blink code indicates that a limit switch is open. The furnace has detected an overheating condition or another open safety circuit and has interrupted burner operation.

Symptoms You May Notice

Burners shut off while the blower continues running; furnace cycles on and off; reduced airflow; unusually hot cabinet or supply air; heating may resume after the furnace cools and then stop again.

Common Causes

Dirty air filter; blocked return air; too many closed supply registers; blower motor or capacitor problem; incorrect blower speed; dirty evaporator coil; restricted ductwork; open high-limit or rollout switch; combustion problem.

Safe Troubleshooting Steps

1. Turn off furnace power. 2. Check and replace a dirty air filter with the correct size and type. 3. Open supply registers and make sure return-air grilles are not blocked. 4. Look for signs of overheating, scorching, soot, or a tripped manual-reset rollout switch without resetting it. 5. Restore power once and observe operation. 6. A qualified technician should verify temperature rise, blower performance, limit-switch operation, duct restrictions, and combustion safety if the code returns.

Parts Commonly Involved

High-limit switch; rollout switches; blower motor and capacitor; air filter; evaporator coil; duct system; integrated furnace control.

When to Call a Technician

Yes if the code returns after checking the filter and airflow, or immediately if there is soot, scorching, a burning smell, or a tripped rollout switch.

Safety Notice

Do not bypass or repeatedly reset a limit or rollout switch. A rollout fault can indicate a serious combustion or venting hazard.

Manufacturer Documentation