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1993 Comfortmaker RPG II Flame Sensor Not Working?

18K views 63 replies 10 participants last post by  Acomfort 
#1 ·
Hi Folks, I see there are allot of knowledgeable Experts so here's my question:

I've already done the removal/cleaning of the Flame Sensor rod, no improvement. Last year I needed a new Ignitor, all is good there.

1.) With the electrical wire attached to the Flame Sensor the 4 Burners will fire maybe 1-2 seconds tops, then turn off and the Control Board flashes 6 times.
2.) With this wire disconnected, I then get the 4 Burners to stay on much longer, maybe 6-7 seconds and then turn off, No Flashing light at the Control Board.
It will repeat exactly like this everytime I try to fire it up.:huh:
Does anyone know where I can find a new replacement Sensor for this Furnace? I've read they can fail. Are these universal? I have absolutely NO manuals, parts lists, info, etc.

How about some expert advice guys? Thank you!
 
#3 ·
Do you think a new Flame Sensor will solve my problem?
I looked on Ebay and found a new one for only $8.00! that looked almost exactly like mine, (just the porcelain sleeve was not as long.)
Not sure about the metal rod length though. I'd love to just buy that and be done with it, but not sure if this would be compatible? I live rurally and would have to drive a bit to a supply house.
 
#5 ·
Clean the front.of the burners first. The flame sensor is just a steel rod for the voltage from the control board to jump through the flame and get back to ground via the burner faces. Voltage present-clean flame sensor-clean burner face and good ground are all needed for the flame to stay on.
 
#6 ·
I removed and checked the Burner, was Clean and fine, maybe a very little light rusty corrosion, no scaling, but other wise fine. I only took this particular Burner off and checked it overall for any obstructions, etc. and I only wiped the Burner face off with my Hand. Are you saying then I need to Wirebrush the little bit of "rusty film" off the actual face of this Burner in front of the Rod, and get it back to bare metal the best I can?

Thanks, Marty S!
 
#8 ·
OK Marty, I will take it apart and try wirebrushing the face of the 4th Burner this weekend and re-post. Tell me this, I found a Flame Sensor on Ebay for only $7.50. It physically looks exactly the same, except the Seller tells me it is 1/2" short in length than mine. (Everything else about it looks identical, small mounting foot and all.) He asked for a specific Model No. and my Furnace has no Nameplate data that I can find. Where is this suppose to be? I've looked all over! So I'm kinda off stuck, but if I need to buy this from him, it would work for me? they all are pretty much universal, like Acomfort suggests, Yes? (Just trying to learn from you guys.) Hopefully the wirebrushing will get me back to normal operation. Thanks again Friend!
I will post my results soon, believe it or not, it's actually getting a bit chilly up here now....
 
#10 ·
Yes, I hope he gets me more detailed info. My Sensor is 2 7/8" lg. below the foot (Burner end) with 2" of it being the metal rod. Yeah, I hope his short end is the wire end. I figure that if the business end is within 1/4" I will be good. When I removed it, I saw it had been cleaned before and about 3/8" of the end was a bit carboned up. The rest was shiny and clean. I wish this guy on Ebay would answer my specific length question, but now it's the weekend; so I guess I'll have to wait on him.
In my "google searching", I saw a website that quoted $139.00 for this sensor, can you even believe it?? They claim it is an exact factory replacement. I'm thinking this Furnace is so old I most likely cannot even get a factory match? There is only the lift off front panel door, a decal saying Comfortmaker RPG II. No other specific data, e.g. Model #, Serial #........ It is 80K BTU, I do know that on a decal glued to the inside sheet metal chassis.
 
#12 ·
New Sensor

OK, guys thanks for the help. I finally got time and found a Sensor that is a very close match; the same dimensions within 1/8" of my old one. I got to say, the industry sure makes it confusing with all these different part numbers for basically the same damn thing! So now I'm good, the part will be here and I will install it next weekend and fire the Furnace back-up. I will also clean the Burner as you guys suggested. I saw where some Utube guy recommended you only need to "rinse the Burners in cold water to clean it?" I will wire brush, then rinse, fire it up and it will then get dry in a hurry. I am just surprised that this Utube guy said "you only need just to rinse them under water"? :whistling2:
 
#15 ·
I believe that. I've only owned this House for 3 years; first time I have ever had a Sensor problem, but when I took this one out it looked "sanded clean" in the flame path from a previous person. But the bottom 3/8" lg. was dirty and carboned up. So yeah, I agree this one must be dead, plus it is most likely the original 1993 sensor.
 
#17 · (Edited)
No Luck

OK folks, I removed and cleaned the Burner, and installed a new Flame Sensor. Furnace is still doing the exact same thing! Damn... (New Ignitor installed last Fall, and it was all running fine then.)

1.) With the Sensor wire attached it will burn for 1-2 seconds, then will go out every time. I then still get the same 6 red flashes every time, after the flame burns out, and then I flip the power switch and try again and again, etc.
2.) Now with the Sensor wire Unattached, the Burners do stay on much much longer, maybe 5-6 seconds, then go out. Why is this? And if I remember correctly, no flashing at all this time at the Control board after the flame goes out. Could my Control Board be the Culprit?
4.) Someone mentioned bad ground, and so I removed the Burner and sanded/wirebrushed the rusty film off the Burner face; and still no progress! I thought for sure this was going to do the job.
5.) I did replace the 24V transformer a few months back. I accidently shorted it out, screwing around and jumping some Control Board terminals, my stupidity. Could I have screwed something up then? I mean the AC works perfectly fine. The control board makes a short clicking sound and then the furnace ignitor starts to glows like always, then the Burners always do come on, but like I said ALWAYS go out quickly.
6.) My AC unit outside works perfectly fine. I've got my new digital Thermostat wired up; the 4 wires from the Therm. to the same matching terminals on the Control board in the Furnace. I've also have the 2 wires coming from the outside AC unit. 1 Black wire going to the "G" terminal on the Control board and the Blue wire to the "Y" terminal on the Control Board. Is this wiring proper for both the Heating and Cooling modes?

I tried to post some pics I took of my Furnace but can't get them to post! I will try pics again in another post.
 
#19 ·
OK guys I know it looks bad and a bit rusty inside. An elderly woman who died there, owned this House before me and most likely didn't know much, you know; but anyhow It seems the Furnace Humidifier was leaking a little bit and I assume that's how some water got inside the Unit over the years. But all is fine, been using it now for 3 Winters. Look at Burner pic, Sharpie written: Unit install 10/5/1993.
 
#21 ·
The 2 wires from the outdoor unit, 1 should go to Y, and the other should go to the C terminal.

Does the error code legend say that 6 flashes is a flame failure error.
 
#26 ·
Ned to open the panel box and check the ground from the furnace to make sure its tight, may also need to check the panel boxes ground.

Did the old transformer have one of its terminals connected to the furnace frame.
 
#27 ·
Looks like there has been some rewiring there. The high voltage side of your transformer looks like both the 120V and the neutral lines are black. Is one of those lines connected to a neutral???

Is the green ground line connected to the 50A50A-112 well connected on both ends?? Can you do a continuity test on that line and connections?
 
#29 ·
120V Power is Black and Common is White Wire, both ends connected well Transformer/Control Unit.
Yes green is good. It is attached/grounded to the frame that hangs the Blower. I also sanded this electrical eyelet connection, plus I even took an alligator clip and extended the ground to a copper water pipe (close by feeding my Water Heater.) I will check to make sure the other end (the plug connector) is not loose.

Can you please briefly explain how to do a Continuity test? Yeah, I do have a meter with the 2 wire probes, but need you to explain if it isn't too involved? I Am learning from you guys!:thumbup:
I just don't understand it, my AC unit works just fine thru the Control Unit, yet I always have Burner flame out when turning the on the Heat..
This Furnace worked just fine until I put in the new transformer. I burnt up the old one screwing around with the Thermostat terminal connections with a jumper wire like a Dummy, but after the smell I figured I burnt-up the Transformer. I Bought a new one on Ebay and all was fine. AC works perfect, but not Heating. I mean the 120V / 24V transformer must not be bad if it is working when I turn the AC on? This new Transformer has a 40v rating, (the old one had a 30V rating). I could not find the exact replacement and I was told this one would work fine. It is pretty much looks/mounts the same in every other way. This would have nothing to do with the Burners?
 
#28 · (Edited)
Gentlemen, thanks for all the suggestions, but Nada, nothing. I even took off the new Transformer and looked at the foot. It was coated with like a plastic film or something, so I took some Emery cloth and sanded that down to bare metal, (like my old one was.) But still absolutely No difference.
I will attach a few pics I took of the transformer and the wiring diagram I made, showing how I have it wired. I've tried switching wires, 120V common and hot sides, and the 24V side as well. But nothing has helped.

What is your Opinion on the fact that all the Burners stay on SO MUCH LONGER, 5-6 seconds at least before Flame out. Then I attach the Sensor wire and the Burners only light for like 1 second! Why is this? Is this telling me anything?
 

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#31 ·
Your new pic's show the transformer neutral as white...My bad.

Do the main burner flames continuously envelope the flame sensor rod for those 5 - 6 seconds of start up?
Do the flames from the burner enveloping the flame rod, look the same as the flames on the other burners?
 
#37 ·
Yes and yes again. I mean all looks exactly as it should! I know because I was involved when we replaced the Ignitor last Fall. So I'm familiar with how she fires and runs. I will say this though, some of the time the first Burner lights and then their is a maybe a 1/4 second, a quick delay before the other 3 Burners light up together. But it's run like that for the 3 years I've owned the place. And yes the flame is a nice Full Blue flame. Thye Sensor Rod is in Full flame like it is supposed to be. Locatiuon and mounting of new Sensor exactly as old one I took out. I've even tried to interchange them. I mean I just don't get it.
 
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