How to Troubleshoot Home Furnace Igniter Problems

Newer modern gas furnaces no longer have a pilot light that the owner must light themselves. Modern gas furnaces have an electronic igniter. If your furnace is not working the igniter could be one of many problems causing the failure. The igniter is not too difficult to troubleshoot and replace if needed. If you are not familiar with gas furnaces or are the least bit unsure of your technical abilities it is advised to call for professional repair. In many cases you can, however, determine the source of your problem. Before beginning any repair or diagnosis you should shut off the gas and electric to the unit you are working on except.....

Gas and electric:

Your furnace will not operate if the gas or electric to it has been shut off. You should verify that the unit has not been disconnected for any reason before making any troubleshooting attempts. You should also check that the thermostat is operational and in the on position for heat. It may sound silly but in many cases the electric switch to the furnace gets shut off by accident and the homeowner wonders why they have no heat.

How the igniter should work:

The thermostat "tells" your furnace that heat is needed and the furnace should turn on.

The blower - inducer motor should begin to turn.

The pressure switch, that senses negative air pressure from the inducer motor, should close.

The inducer motor may run for up to thirty seconds before gas flow starts.

The igniter should glow and the flame sensor should sense the flame from the igniter.

When the flame sensor senses the flame from the igniter, the burners will come on and the heating cycle will start.

Checking and replacing the igniter:

If the igniter does not glow the flame sensor will not allow the gas to remain on. The first quick and easy determination for this is if you need to electrically turn your furnace off and then back on continually to get it to run. In many cases the blower motor will continue to run without any heat causing your home to actually be colder.

At this point in your inspection you should have your furnace manual or an on-line pictorial source. Be sure to shut off the gas and electric now. Examine the igniter, identified by your manual, but do not touch the glass portion with your bare hands. Oil residue from your hands can cause a working igniter to become non-working. If you see any cracks of any size you need a new igniter. New igniters are relatively low in cost and not exceptionally difficult to replace. Even so you may wish to have professional repairs done but you will know in advance what to expect.

If you do not see any cracks in the igniter you may very well have a different problem. Your furnace may not be working due to a bad control board, dirty or bad flame sensor or bad limit or roll out switches.

References:

http://arnoldservice.com/Troubleshooting_Heating_Problems.htm

http://home.howstuffworks.com/home-improvement/heating-and-cooling/how-to-maintain-a-furnace1.htm

Author's mother, who wondered why they had no heat when they had inadvertently turned off the furnace switch.