How to Troubleshoot a Furnace Ignition

A furnace is rarely used over the warm summer. Most of us don't bother to inspect our furnaces until the first sudden cold day of winter, when it is too late to do major furnace repairs. One common problem involves the ignition system on gas furnaces. The pilot flame that ignites the furnace may need adjustment, or worse, it may have gone out entirely. Either of these problems are quite easily repaired, with heat restored after only a short time.

Things You'll Need

• Flashlight
• Matches (long-handled wooden)
• Needle
• Wire brush

Instructions

1. Turn off any electric power to the furnace (there is usually a power switch near the unit). This renders the furnace inert so that the pilot ignition can be safely worked on, with no chance of electric shock. It also ensures that the furnace doesn't go into operation when the parts are removed for cleaning.

2. Check the gas pilot light. When the front service panel is removed, if the pilot light is working, the flame should be clearly seen. If there is no flame, attempt to relight it following the printed instructions on the furnace (don't forget to turn the gas off for 3 minutes first, as instructed). If it holds when relit, look at the flame for color and intensity.

3. Check for the proper color flame. A well-adjusted pilot light flame is blue (for natural gas) or green (propane) and straight. Yellow coloration in the flame, and/or a bend in the flame, means that the unit must be cleaned. Yellow or blue tips in a blue flame are not a concern; don't exhale close to the nozzle, since this can color the flame. If the flame appears split or forked, this may be caused by dirt in the pilot tube.

4. Check and clean the pilot nozzle if the flame is yellow or bent. First turn the gas valve off. Use a wire brush to gently clear the nozzle of debris or deposits. Use a needle to remove dirt from the pilot tube.

5. Relight the pilot again and check the flame quality. Manipulate the gas valve until the optimal flame profile settles in. If the pilot light simply won't light or won't stay lit, the thermocouple might need adjustment or replacement, which should be done by a professional.

6. Check the actual operation of the ignition system. Once the flame is burning blue (this may take a few moments), replace the cover panel, restore the furnace's electric power and watch it operate for a few moments through a full cycle including heating, blower on, heater off and blower off. After completing the troubleshooting checklist above, the unit should move smoothly between ignition and the operation cycle.

Tips & Warnings

• Take off the service panel, from time to time, and watch the furnace operate for at least one entire cycle. Keep the area in front of the pilot clear from dust and dirt. Call the local gas company before arranging repairs. Some companies provide basic repairs free of charge.

• It's vital to have the ignition system and furnace inspected at least every 3 years by a service person, more frequently if the furnace is more than 10 years old. Major defects in the ignition system occur in older furnaces.

Resources

• Economic Expert: Listing of many U.S. gas companies