Goodman Gas furnace

Anthony Mobilio_3

Did a no heat call today. The burner would fire and go off. After a few times the LCD display came on flashing once. Looked it up on the door it said the flame sensor was no good. I replaced it and it works. What is the best way to test the flame sensor to see if it's ok.


Thanks A

masterplumb

Flame sensor

Usually when the burners ignite and then shut off, it is the sensor. Chris

John Mills_3

Put a DC microamp meter in series with the flame rod. Most need nearly 1 microamp to prove flame though usually a clean sensor will provide over 3 microamps.

Unknown

You probably only

needed to clean the sensor with soft clean emory cloth instead of replacing it. It would only need replaced if it was damaged.

John Mills gave you the procedure for checking microamps. The usual range on most systems is 2 to 10 microamps.

Dale

Most flame sensor problems

Timmie is correct about most flame sensor problems, we use a scotch brite dish pan cleaner to polish them. The usual problem is a thin coating of invisible laundry chemicals that plate the sensor. The problem you described can be from alot of other sources like reversed polarity or poor ground. While the flame sense micro amp reading is a good idea, easily done with a better meter like a fluke 16, remember that the meter senses dc flow and the problem can be in the control box part of the circuit. A ohm check is usually a good first start, if continuity from box end to flame tip the cleaning will fix the problem 90% of the time. The closer the furnace is to the washer the more to suspect it.

Anthony Mobilio_3

How does the flame senser keep the unit running with the dc volts...

Thanks

Unknown

DC Microamps

is created by passing a AC voltage through the flame and rectifying the AC signal to pulsating DC measured in microamps. It is possible by using the ionization of the molecules in the gas and creating a greater ratio to ground through the flame than rod area, it must be 4 times greater ground to flame rod. This is called FLAME RECTIFICATION. The elecronic controls used on systems have circuitry designed to detect that signal and when that signal is present it triggers a microprocessor circuit which in turn will activate circuitry to the gas valve to cause it to open. All of this is accomplished with intermittent pilot 24 volt systems. It is also possible with Hot Surface Igniters either using the igniter as a sensor or using a seperate "Kanthal Steel" flame sensor. A similar feature with Direct Spark Ignition Systems does the same thing.

If you are interested in more information I have a number of manuals available that explain this in detail.