A gas furnace that keeps lighting and then shutting off, only to repeat this cycle, can be caused by several issues related to the furnace’s safety features, ignition system, and airflow. This article will explore the specific reasons and technical explanations for this problem, as well as provide troubleshooting steps and cost estimates for potential repairs.
What Causes a Gas Furnace to Keep Lighting and Going Out?
1. What is the Issue with the Flame Sensor?
The flame sensor is responsible for monitoring the burners to ensure a flame is present. If the sensor is dirty or corroded, it may not detect the flame, causing the furnace to shut off even when there is a flame. Cleaning the flame sensor with a soft abrasive pad can resolve this issue. If the problem persists, the flame sensor may need to be replaced.
2. What are the Ignition System Problems?
The ignition system can also be the culprit behind a gas furnace that keeps lighting and going out. A faulty ignitor might fail to maintain a continuous electrical path, causing the burners to shut off shortly after ignition. Testing the ignitor for continuity with a multimeter can help diagnose this issue. Additionally, a malfunctioning gas valve could prevent the gas from flowing properly, causing the pilot to light but then shut off immediately.
3. How Can Airflow and Venting Issues Affect the Furnace?
Low airflow can cause the furnace to overheat, triggering the limit switch to shut off the furnace. Ensuring proper airflow by cleaning or replacing the furnace filter and checking for blockages in the ducts is crucial. Issues with the exhaust vent fan or its sensor can also prevent the furnace from operating correctly.
4. What Control Board and Wiring Problems Can Cause the Furnace to Shut Off?
The control board, which is the brain of the furnace, might be malfunctioning due to disconnected or frayed wires, preventing it from sending the necessary signals to other components. Voltage fluctuations to the ignition control board or gas valve can also cause intermittent operation.
5. How Can the Pressure Switch and Draft Inducer Motor Affect the Furnace?
The pressure switch ensures adequate airflow before allowing the furnace to ignite. If the switch is faulty or if there is insufficient airflow, the furnace will not ignite properly. Similarly, if the draft inducer motor, which draws air into the furnace, fails, the furnace will not ignite correctly.
Troubleshooting Steps for a Gas Furnace that Keeps Lighting and Going Out
- Check Error Codes: If your furnace has an error code display, check the codes to narrow down the problem.
- Inspect and Clean Components: Clean the flame sensor, furnace filter, and ensure proper airflow.
- Test Components: Use a multimeter to test for continuity in the ignitor, limit switch, and other components.
- Bypass Sensors Temporarily: Bypass the exhaust vent fan sensor or other sensors to see if the furnace operates normally.
Estimated Costs for Repairs
- Flame Sensor Replacement: Typically inexpensive, around $20-$50.
- Ignitor Replacement: Can range from $50-$200 depending on the type and brand.
- Gas Valve Replacement: More costly, potentially $200-$500 or more.
- Control Board Replacement: Can be expensive, often $200-$1,000 or more.
- Draft Inducer Motor Replacement: Costs vary but typically range from $100-$300.
Recommended Tools or Products
- Multimeter: For testing continuity and voltage.
- Soft Abrasive Pad: For cleaning the flame sensor.
- Furnace Filter: Regular replacement is essential for maintaining proper airflow.
