Relighting a furnace can be straightforward for some systems and hazardous for others. This guide explains how to relight your furnace safely, whether you have a standing-pilot gas furnace or an electronic ignition. It also covers essential safety precautions, common issues, and maintenance tips to prevent future relights.
Understanding your furnace type and following precautions helps homeowners address minor relight issues confidently while knowing when to call a professional.
Identify Your Furnace Type
Knowing your furnace type helps determine the correct relighting steps and safety precautions.
Standing Pilot Gas Furnaces
- Turn off the thermostat to prevent a heat call while you work.
- Locate the gas shutoff valve near the furnace and turn it to OFF.
- Wait 5–10 minutes to clear any accumulated gas.
- Remove the lower front panel to access the burner and pilot assembly.
- Set the gas control knob to OFF, then rotate to PILOT.
- Hold the knob in place and light the pilot with a long match or the furnace’s built-in igniter if available.
- Continue to hold the knob for 30–60 seconds after lighting to heat the thermocouple.
- Release the knob and verify the pilot light stays lit. If it goes out, repeat once more.
- Turn the knob to ON and replace the access panel. Restore power to the thermostat and set it to your desired temperature.
- If the pilot won’t stay lit after multiple attempts, or you smell gas, leave the area and call a professional immediately.
Intermittent Pilot / Electronic Ignition
- Set the thermostat to heat and a low temperature to minimize calls for heat.
- Ensure the furnace door or access panel is properly in place; check that the power switch is ON and the circuit breaker is not tripped.
- Confirm the gas supply to the furnace is open and there is no gas odor in the area.
- Intermittent pilots and electronic ignitions usually light automatically; there is no manual pilot to relight. If ignition fails, proceed to the reset steps below.
- Reset the furnace by turning off the power switch or the circuit breaker for about 30 seconds, then restore power and try again.
- If the furnace still does not ignite after a reset, check for error codes on the control board or thermostat and consult the owner’s manual.
- Persistent failure to ignite or frequent cycling indicates a faulty igniter, flame sensor, gas valve, or control board and warrants professional service.
Safety Precautions
- If you smell gas, leave the area immediately and call your gas utility or emergency services from a safe location. Do not light anything or use electrical switches in the area.
- Never attempt to light a standing-pilot or intermittent-pilot furnace if you are unsure of the procedure. Follow the manufacturer’s instructions from the manual.
- Turn off the gas supply at the appliance valve before performing any maintenance. Ensure adequate ventilation during and after relighting attempts.
- Wear safety glasses and protect your hands; keep children and pets away from the work area.
- If you suspect a damaged thermocouple, cracked burner, or unusual burner flames (yellow or orange rather than blue), stop and contact a professional.
Troubleshooting Common Issues
These are frequent problems homeowners encounter when relighting a furnace and practical steps to address them, while recognizing when to seek professional help.
- Pilot won’t stay lit: This often points to a dirty or faulty thermocouple, gas valve, or gas pressure issue. Clean or replace the thermocouple if you’re comfortable, but if the flame still dies, call a technician.
- No ignition in electronic systems: Check that the thermostat is calling for heat, the furnace power is on, and the gas valve is open. If these are correct and ignition still fails, reset the furnace. If it still fails, professional service is needed.
- Flames are yellow or flicker: Yellow flames can indicate poor gas mixture or venting problems, which require inspection by a pro. Do not attempt to adjust gas pressure yourself.
- Repeated short cycling after relight: Could be a dirty flame sensor, blower motor issue, or control board problem. Clean the flame sensor if you know how, but persistent cycling should be diagnosed by a pro.
Maintenance And Prevention
Regular maintenance reduces the likelihood of future relighting problems. The following practices help keep a furnace reliable and efficient throughout the heating season.
| Task | Frequency | Notes |
|---|---|---|
| Replace or clean furnace air filter | Every 1–3 months | Maintains airflow and efficiency; a clogged filter strains the system. |
| Annual professional furnace inspection | Yearly | Technician checks burners, heat exchanger, venting, and safety controls. |
| Test carbon monoxide detectors | Every 6–12 months | Ensure detectors are functional in living areas and near sleeping spaces. |
| Inspect flame sensor and burners | During routine service | Clean or replace as needed to prevent ignition issues. |
| Check thermostat batteries and settings | Every 6–12 months | Reliable readings prevent incorrect heat calls. |
Always follow the manufacturer’s instructions specific to your model. If a relight attempt fails or you notice signs of gas problems, contact a licensed HVAC professional. Regular maintenance not only reduces relight frequency but also improves safety and efficiency.