What This Error Means

Error code 34 means flame was not sensed during the ignition trial or the flame signal was lost during steady operation. Repeated failures can lead to ignition lockout.

Symptoms You May Notice

Inducer starts; igniter operates; burners fail to light or light briefly and shut off; repeated ignition attempts; code 34 flashes; furnace may later enter code 14 ignition lockout.

Common Causes

Gas supply off or inadequate; dirty or damaged flame sensor; failed or mispositioned igniter; poor burner crossover; loose ignition wiring; improper grounding; unstable flame; gas valve problem; faulty furnace control.

Safe Troubleshooting Steps

1. Confirm the thermostat is calling for heat. 2. Verify the manual gas shutoff valve is open if you know its location. 3. Turn off furnace power before inspecting panels. 4. Look for an obviously loose flame-sensor or igniter wire. 5. Do not touch or reposition the igniter. 6. Restore power once and observe whether the burners light and remain on. 7. A technician should test ignition voltage, gas pressure, flame-sense current, grounding, burner crossover, gas valve operation, and control outputs.

Parts Commonly Involved

Hot-surface igniter or ignition device; flame sensor; burner assembly; gas valve; ignition wiring; grounding; integrated furnace control.

When to Call a Technician

Call a technician if the burners do not light, the flame shuts off repeatedly, code 34 returns, or the furnace enters ignition lockout.

Safety Notice

Do not continue resetting a furnace that cannot prove flame. Leave the building and contact the gas supplier from a safe location if you smell gas.

Manufacturer Documentation