How to test flame sensor


<a href=”Lennox 28M97 Angled Flame Sensor For Mpga Cmpe Cmpb 20467102 ” title=”flame sensor amazon”>How to test flame sensor

In the picture you will see a 1/8 inch round rod in the flame, that is the flame sensor. You need a multi meter that measures micro amps which you will connect in series with the flame sensor. The sensor is usually located on left side but on some furnaces it may be on the right side.

How the flame sensor works is by a small AC electrical charge going through the sensor and it uses the flame to carry the electrical power to ground. Burner surface to flame sensor is 4:1 ratio thus causing the AC current to change to DC current. If no flame present, dirty flame sensor, bad flame characteristics similar to flame lifting off or carbonizing there will be low or no micro amp draw and the control board will shut the flames off. After 3 to 5 tries the control board will lock the furnace out for 3 hours, which can be reset by cycling power or thermostat.

All furnaces have different micro amp readings some good at .8 while others need 6 you will need to find out the right micro amp reading for your furnace. The flame sensor has a coating on it to make it last a long time and will get worn off by over cleaning, so it is best to only clean rod when it is needed. If flame sensor requires cleaning more often then once a year it should be replaced, or check for other problems like vent stack temperature, gas pressure, or primary air need to be adjusted.

How to clean flame sensor

  • First find the flame sensor.
    Most furnaces you will find a white wire located on the left side connecting the flame sensor to the circuit board.
    Watch the furnace ignite you will see spark or orange glow in front of one burner and the flame sensor should be on opposite side, but I have seen them on the next burner from the igniter.
  • Shut power off to the furnace while you are working, you will find a light switch high on wall or in the ceiling.
  • Most furnaces have 1/4 inch screw that holds the sensor in place; any multi screwdriver without the bit will be 1/4 inch. Remove the screw(s) and disconnect wire
  • Once removed you can clean the sensor with a scotch brite pad, if you do not have one then just use a clean rag for now. Do not use sand paper or wire brush, as it will remove the protective coating and scratch the rod causing it to fail more often. Some people like to clean every year but I advice not to, It is best to clean only when needed since the protective coating will be removed with over cleaning
  • Once the rod is cleaned reconnect the wire and screws making sure the rod sits in the flame. Some times the burner and any grounding surface will get dirty and need to be cleaned as well.

Click here to see my post “first check thermostat”
Click here to see my Post on protecting your home “Alarm for home”

Thank you for visiting my blog I would appreciate any feedback I can get, Please leave a comment on whether my information has helped you. I am always interested in more topic to write so feel free to leave a comment asking about anything related to HVAC-R (Heating, Ventilation, air conditioning, refrigeration).

Thanks for reading my blog

link in picture to amazon parts

7 thoughts on “How to test flame sensor

  1. inommattVox 12/09/2012 at 6:42 am Reply

    You made some decent points there. I looked on the web for the concern and found most individuals will go along with along with your website.

    Personalized NFL Jerseys

    • jetstrem 12/18/2012 at 8:48 am Reply

      Thanks for your comment, I try to make things easier for everyone to help them determine what is wrong and to make repairs. Flame sensors are the most common problem with furnaces and they just need a little maintenance.

  2. Mike 11/13/2013 at 7:40 pm Reply

    I have a Magic Chef G6A75D-11 that is exhibiting symptoms indicative of a faulty flame sensor (blowing intermittently, not responsive to thermostat temp changes). The furnace is VERY old though I do not know exactly how old, at least 20 years…at least. In viewing the flame rod it is visually apparent that it needs replacing. The flame rod appears to be crumbling and is jagged at the tip.

    I am having trouble finding a replacement. Are flame rod’s generally interchangeable among different models?

    The gas valve assembly is manufactured by Honeywell for this model.

    Any help is greatly appreciated.

    Mike

  3. Vimax 11/16/2013 at 9:35 pm Reply

    Keep working ,great job!

  4. Tony Gallegos 11/25/2013 at 11:59 am Reply

    Thank you very much. You are spot on. I am an electrical engineer- so I understand the concept well. Some yahoos have posted that a flame sensor measures heat and thus puts out millivolts. No- that’s a thermal couple. A flame sensor measures current through the flame, so series current must be read. Very good- Take care.

  5. Interior noise measurements 12/07/2013 at 7:42 pm Reply

    Your style is very unique in comparison to other folks I have read stuff from.
    I appreciate you for posting when you’ve got the opportunity, Guess I will just bookmark this
    page.

  6. Scott 02/03/2014 at 2:51 am Reply

    Thank you for being so thorough. Over the past few years and certainly yesterday I have sanded off the protective coating. I’ll start the hunt for a replacement.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

Follow

Get every new post delivered to your Inbox.

%d bloggers like this: