Bench testing flame sensors?

[chaser310]

I have a hand full of f/s . Was just wondering can they be tested out of a furnace with just a flame (torch or lighter) and meter? Kind of like testing a t-couple on a bench? If not I will just check them on the shop furnace.

Thanks

[DeHeatify]

I would think that if you simulate a flame rectification circuit by sending like 90 to 120 volts through the flame sensing rod and having it ground out on something similar to a burner face with flame in between and your meter hooked up, in theory that should work.
I would expect you would only get accurate results if the flame used was similar to a burner flame though; and the ground similar to 2, or a used burner.
I'm really just guessing here though

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[Mr Bill]

I would think that if you simulate a flame rectification circuit by sending like 90 to 120 volts through the flame sensing rod and having it ground out on something similar to a burner face with flame in between and your meter hooked up, in theory that should work.

What! am I missing something here?

[DeHeatify]

Probably not... I may be missing a few screws! Maybe i shouldn't answer things first thing in the morning. . : }

In rereading.. it should say "and the ground similar to a burner.. or use a used burner" so I guess that would basically be saying. No...why bother.

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[hvac69]

A flame sensor is not a magical device it is nothing but a metal rod with a ceramic or porcelain insulator. If you have continuity from the tip to the electrical connection, clean from excessive dirt and the insulator is not cracked it is good.

[air1]

Does anyone know what voltage is used in a typical furnace flame rectification circuit? Is it actually 120VAC? If so, I'm glad I never tried to touch the sensor while a furnace was try to ignite. I've measures many flame rectification circuits with my meter but have never be bitten by one.

[martyinlincoln]

Depends on the control board air1. Put one meter lead on the flame sensor wire and the other to ground and check a few. It only takes a second. BTW the voltage is not only present when it's trying to light. Many boards send constant voltage to the flame sensor,checking for flame when there should not be one.

[hearthman]

You can test flame rectification with most any voltage. I know of fireplaces that use a 3vdc system. It is the microamperage that counts. In order to test a flame rod in addition to a stable flame that closely approximates that of the subject appliance, you would need a ground that has a mass at least 4x that of the rod. Note that a rod which tests ok out of the unit does not guarantee it will work once installed so I see little benefit to this bench testing. As long as ceramic insulators are not cracked, there isn't much else to go wrong other than the actual electrical connections.

[LKJoel]

Interesting thread

Could you mount it next to a burner flame and use the diode checking function on your meter, testing between the burner ground and flame rod lead?

That may be a simple test, but I have never tried it

You have sparked my curiosity though

[LKJoel]

As long as ceramic insulators are not cracked, there isn't much else to go wrong other than the actual electrical connections.

I was always told that flame sensors had a coating on them that helped the flame rectification, and that if it was damaged, it would not pass through the correct flame signal

Is this accurate? Or was somebody misinformed

[MicahWes]

It is just a metal rod. This is somewhat oversimplified, but it just completes a circuit through the flame itself to prove ignition.

[Core_d]

I can't get a uA reading on my home furnace at all. Its an janitol with a spark igniter. flame sensor is coming from ignition module i know its good if i unplug it durners shut down and spark starts up and i know my meter is good ive tested the sensors at my school the same day. This has been bugging me can anyone please give me an explanation?

[littlebigdad]

Maybe I'm doing something wrong but I haven't replaced maybe a dozen flame sensors in 25 years