If you have a meter that will measure micro amps then you can test the flame sensor with a multi-meter. Below we have a YouTube video made by Grayfurnaceman which shows how to test a flame sensor using a multi-meter. Thanks to Grayfurnaceman for making this informative video!
We have seen many furnace flame sensor problems in our 25 year old HVAC business. This can be an easy fix which could save you lots of money and keep you from spending a cold night in your home. We have received hundreds of customer testimonials telling us how our customers have repaired their furnaces by cleaning or replacing the flame sensor. Here is the problem with the solution. Please keeep in mind that most of the time it is the flame sensor that is causing the problem, but sometimes it can be a control board problem or another furnace control problem.
Problem: Your furnace main burner ignites, the main burner stays on for 8 to 10 seconds, then shuts right back off. Your furnace tries this ignition sequence again, and the same thing happens. After 3 times the furnace goes into lock out, and the only way to get it out of lock out is to turn the power switch off and on. Everything starts over again without ignition of your gas burners.
Solution: First, turn off the power to your furnace. Check all wires and ground wires to make sure they have good tight connections and are not burnt. Next, remove the screw or screws that hold your flame sensor in place. Please do not confuse the flame sensor with an Ignitor. We do not want to touch the ignitor at all. If you touch an ignitor it can shorten the life of the ignitor or it could break. Clean your flame sensor with steel wool or emery cloth (fine sand paper). If you have a meter that will measure micro amps then you can test the flame sensor with a multi-meter. Below we have a YouTube video made by Grayfurnaceman which shows how to test a flame sensor using a multi-meter. Thanks to Grayfurnaceman for making this informative video! You might need a new flame sensor, but most of the time they can be cleaned and your furnace will work after cleaning. I have seen flame sensor go out. Most of the time when they go out the white porcelain is cracked. You might want to have a spare flame sensor on hand. Below we have links to the various name brand furnace flame sensor pages where you can purchase a new flame sensor. We only sell brand new OEM flame sensors. If you have any questions please email us anytime. Our email address is: firstname.lastname@example.org. We would love to help you out and have your business!