flame sensor, how does it work?

[ghaddox]

how exactly does a flame sensor work? NOT the old MFS but the single wire ones.

[bb]

Do a search for flame sensor.

Here's one to get you started
http://hvac-talk.com/vbb/showthread.php?threadid=45541

[spotts]

if flame is touching it, elect. passes through the carbon in the flame, back to the burner.... Flame sensed.

If electricity doesn't leave that rod due to no flame or corrosion insulating it, flame not sensed.

[Carnak]

The flame rod is small compared to the burner.

Alternating current goes to the rod and it will flow through the flame by "ionization" to the burner head.

Because the current alternates, current is trying to go back from the burner to the rod.

It is easy for the little rod to "hit" the big burner with current however it is hard for the big burner to "hit" the little rod with current.

Because of this, current tends to only travel from the rod to the burner. It is like a half wave rectifier, similar to putting AC current through a diode and only getting pulsating direct current out.

If the flame signal monitored by the gas control was alternating, it would shut off as it would mean there was a short.

[seanyb1]

I don't understand all of your explanation. My burner is lighting, but the brand-new flame sensor is not sending the signal to the controller unless I run the propane/air mixture excessively rich. Can you elaborate any further.

[hurtinhvac]

I don't understand all of your explanation. My burner is lighting, but the brand-new flame sensor is not sending the signal to the controller unless I run the propane/air mixture excessively rich. Can you elaborate any further.

Call a technician for God's sake. Or we'll see you on the news or the Dark Side of the Moon.

[bkenn]

I suggest that the rectification is due to the probe being hotter and shedding electrons, rather than electrons "finding" the larger object. The old electronic vacuum tube "valves" used that to great effect.

[ckartson]

You asked how a flame rod worked, you got very good explanations of exactly that. There is more to a system than a flame rod. Now we find out why you asked. Call for service.

[seanyb1]

Unfortunately, there are no service technicians available in my area. The explanation was rather nebulous- I now understand that current flows from the rod through the flame and on to ground via other research. The snarky responses are not appreciated.

[ALASKAFISH]

"YE SHALL KNOW THE TRUTH, AND THE TRUTH SHALL SET YOU FREE" I agree that Snarky responses are no substitute for customer relations. It's not the facts (truth) that provides us with answers, It is knowledge of the truth. Unfortunately, the ability to convey knowledge regarding technical facts to a homeowner or customer is limited by the technicians ability to be free in his or her knowledge. As you have discovered, the words Flame Sensor are self explanatory. Flame sensing is a part of the "sequence of and is necessary for proper operation"

Unfortunately, there are no service technicians available in my area. The explanation was rather nebulous- I now understand that current flows from the rod through the flame and on to ground via other research. The snarky responses are not appreciated.

[twodotmike]

check out the explanation on the site http://hvacwebtech.com/Flame%20Rectification.htm

[earlburnermann]

This is not a do it yourself site. You got an explanation about how flame sensors works and you also received links for further study. What you won't get here is help blowing up your home and family. Look harder for a service tech.
http://www.youtube.com/watch?v=M5QGk...e_gdata_player

[hurtinhvac]

"The heater then opens the gas valve. This signals the igniter which, when it hits the gas, will turn into a flame."

Wrong.

"However, when these systems use the same hot surface igniter for sensing and ignition"

Wrong.