Furnace Starts then Stops - How To Clean a Flame Sensor and Why

Introduction

This tutorial will guide you through the process of cleaning the flame sensor in your furnace. If your furnace starts but then stops, or if you're getting ignition failure codes, a dirty flame sensor might be the culprit. Keeping this sensor clean is essential for the proper functioning of your furnace.

Step 1: Gather Necessary Tools and Materials

Before starting, make sure you have the following tools and materials ready:

• Multimeter (e.g., Amprobe ACD-14 PLUS)
• Electronic test leads (e.g., Meterk Digital Multimeter Leads)
• Cleaning brush (e.g., Pro Shot Gun Brush-Bronze)
• Screwdriver (flathead or Phillips, depending on your furnace)
• Safety gloves and goggles

Step 2: Turn Off the Power and Gas Supply

Safety is paramount when working with furnaces. Follow these steps:

1. Locate the furnace power switch and turn it off.
2. Turn off the gas supply to the furnace. This is usually located near the furnace and has an on/off valve.

Step 3: Access the Flame Sensor

To clean the flame sensor, you will need to locate it:

1. Remove the access panel of your furnace using a screwdriver.
2. Identify the flame sensor, which usually looks like a small metal rod located near the burners.

Step 4: Remove the Flame Sensor

Carefully detach the flame sensor for cleaning:

1. Use a screwdriver to unscrew the flame sensor from its mounting bracket.
2. Disconnect the wire lead attached to the sensor.

Step 5: Clean the Flame Sensor

Cleaning the flame sensor is crucial for its proper function:

1. Use the bronze brush to gently scrub the surface of the flame sensor. This removes any soot or debris.
2. Ensure that the sensor is clean and shiny after brushing.
3. Avoid using any harsh chemicals as they can damage the sensor.

Step 6: Reinstall the Flame Sensor

Once cleaned, reinstall the flame sensor:

1. Reconnect the wire lead to the flame sensor.
2. Secure the sensor back in its mounting bracket with the screwdriver.
3. Ensure it is tight but not overly forced.

Step 7: Restore Power and Gas Supply

After everything is reassembled, turn the power and gas supply back on:

1. Turn on the gas valve.
2. Switch the power back on at the furnace.

Step 8: Test the Furnace

Finally, test the furnace to ensure it operates correctly:

1. Set your thermostat to call for heat.
2. Observe the burners to see if they ignite and stay lit.

Conclusion

Cleaning the flame sensor is a straightforward process that can resolve common issues like ignition failure and burners shutting off. Regular maintenance can help ensure your furnace operates efficiently. If problems persist after cleaning, consider consulting a professional HVAC technician for further assistance.