Bryant 90 Plus furnace won't stay lit


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Old 10-10-12, 07:59 PM
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Bryant 90 Plus furnace won't stay lit

Let me back up some here. Last week furnace started acting up but it was only on for short periods because the weather was nice. This last weekend furnace would not run. I was getting the continuous blinking LED for reverse polarity. Polarity was fine and after searching the web I thought I needed a new board. I tried everything and on a last try I reversed the 24v from the transformer on the board (polarity??) and the furnace went through the startup sequence. Finally!! Then it went out after a few seconds. Uggh...Error code 34 then 14. I had read about cleaning the flame sensor for that error, so I did that and then put everything back together, ran it through the start up sequence again and we have fire!! Nice blue flame. Ran that way for two days and now I am back to error 34 for 3 times then lockout error 14. What else could be doing this? I have read things on the pressure valve and Vacuum Sensor, just not sure how to narrow the problem down and verify. Heat sensor limit switch seems fine, it doesn't seem to be tripped. It doesn't do any thing when you push on it. It isn't sticking out or anything. Furnace venting seems fine also can feel intake and exhaust outside. This summer was brutal on the AC and I do notice we had alot of condesate this year. I did clean out the condensate line above the burners and the furnace in the heat duct top as it was clogged. I thought maybe that was it but no go... help.
 
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Old 10-10-12, 08:05 PM
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Reversing the wires didn't really affect the problem since a/c has no polarity. Just a co-incidence. I have not had the best of luck cleaning the flame sensor rod. If I suspect that's the problem I replace it.

You said the code is telling you reverse polarity. I believe that refers to the A/C wiring to the control board. If you have a meter (preferably analog-not digital) check from the white wire to metal case on furnace......should show 0 volts. Black wire to metal case should show 110Vac
 

Last edited by PJmax; 10-10-12 at 08:21 PM.
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Old 10-10-12, 08:19 PM
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Why would the flame sensor work for two days after being cleaned and then not work suddenly? I read they don't ever really go bad as they are just a big thermocouple. Any other ideas? Any way to test flame sensor?
 
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Old 10-10-12, 08:29 PM
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A single wire flame rod is NOT a thermocouple. The job of a modern flame sensing rod is to become part of a closed loop balanced circuit. The flame itself actually causes a short from ground to the flame rod. The rod is made up of different alloys that react a certain way in the presence of the flame.
 
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Old 10-10-12, 08:35 PM
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In order to check the flame rod you need to measure the current on it. To do this you need a microammeter in series with the rod.
A bad ground is a common cause for the problem you are experiencing.
 
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Old 10-10-12, 08:36 PM
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It's very important that the flame-sensing rod works properly. Dirt, corrosion, or bad connections in the flame-sensing circuit can cause the controller to think the flame didn't ignite, and the gas valve will be shut down prematurely. You'll need a meter capable of reading 10 microamps of current. You'll put the meter in series with the rod and its supply line to the module.




on edit....Tag grady.....you're it.
 
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Old 10-10-12, 08:51 PM
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Ok Thanks to both of you. My meter doesn't do Milliamps, so I wil get one from work tomorrow. I am preety sure the Fluke 87 does it. Thanks! I'll let you know. Any other possibiliies?
 
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Old 10-10-12, 08:54 PM
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How many milliamps should I read if it is good or bad?
 
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Old 10-10-12, 09:12 PM
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You should read around 5-6 microamps higher is definitely better. Under that and it's borderline.
 
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Old 10-10-12, 09:28 PM
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I actually looked at my meter at home closer and it will do microamps (uA). I get 1.3 with the system powered but no flame and 7-8 microamps once flame is present. I get 10-11 microamps at flameout. Sounds like it is ok??? Any other ideas to check that I am missing?
 
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Old 10-10-12, 09:58 PM
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Sorry to nitpick you when it's not especially important, but I find the flame rectification system interesting, so I like to explain it.

The flame sensor is usually energized with AC voltage whenever the inducer motor is operating. Since there is no complete circuit there is no current flow.

With the proper AC voltage applied to the flame sensor and the flame sensor engulfed by flame, there is a complete circuit from the flame rod to ground through the flame. But the flame rectifies the AC voltage and the flame produces a high resistance, so only a few microamps of DC current flow.

By ohms law, R= E/I. The voltage is usually 24 VAC and the current flow through the flames is usually about 6 microamps (6/ 1,000,000). That give a resistance through the flame of four million ohms.

The metal content of the flame sensor is not important for flame rectification. It is the flow of current through the flame that causes the current flow. You can attach the wire from the flame sensor to a screwdriver and the flame sensor circuit will work when the screwdriver is in the flames.

This is similar to an old vacume tube diode that rectified an AC voltage to a DC voltage.
 
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Old 10-10-12, 10:14 PM
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I actually looked at my meter at home closer and it will do microamps (uA). I get 1.3 with the system powered but no flame and 7-8 microamps once flame is present. I get 10-11 microamps at flameout. Sounds like it is ok??? Any other ideas to check that I am missing?
Interesting....with no flame there shouldn't be any reading since you're reading the current of a loop that is open.
 
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Old 10-10-12, 10:17 PM
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Should I be looking for AC or DC microamps through the flame rod sensor?
 
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Old 10-10-12, 10:18 PM
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The flame rectifies the a/c into dc. So you should use DC.
 
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Old 10-10-12, 10:47 PM
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OK so I get 3 uA at flame up but after about a 2 seconds it gets to 5.6 uA then flame out maybe 1 sec later. How quickly is the circuit looking for 5-6 uA??
 
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Old 10-10-12, 10:58 PM
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I don't know exactly but it's under 5 seconds.
Good....now that you have the meter in line you can experiment a little. Try using a scotchbrite pad to polish the burner in the sensor area. Check your reading. It should increase. Try changing the space between the flame rod and the burner. Closer and farther. Go easy...don't snap anything. Watch your readings. You're looking for the highest possible reading.
 
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Old 10-10-12, 11:23 PM
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Tried to go easy, but trying to bend out and it cracked at the bend. Guess now it gets replaced. Get one tomorrow. Good thing it's not cold yet. House will stay warm enough. More info tomorrow.
 
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Old 10-11-12, 02:00 AM
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Your reads are peculiar. You should get o uamps with no flame and with a clean flame sensor 5-7 uamps with flame present.

I don't know what you cracked --- was that the flame sensor wire?

Try measuring the AC voltage being applied to the flame sensor wire when the inducer motor is running. What is the voltage and is the voltage steady or does it vary?

Erratic performance of the kind you describe suggests a failing circuit board that needs to be replaced, but some additional testing of the kind described above might help prove that.
 
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Old 10-11-12, 05:35 AM
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My Flame Sensor Rod is mounted below the burner and the rod has about a 45 deg bend in it to get it up into the flame. PJmax wznted me to bend it slightly to get it closer or farther away. Then alloy is obviously not very flexible at least after 20 winters of being heated. Got to get a new one. Hope it solves the problem.
 
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Old 10-11-12, 09:34 PM
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how did you have your meter installed to check the flame signal.

1 lead should have been on the flame sensor spade terminal, the other lead should have been on the wire that would have been attached to the flame sensor.
http://youtu.be/VfOwPvgf7w4 Trane Presents Measuring Flame Sensor Current.mp4 - YouTube
 
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Old 10-11-12, 11:04 PM
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I split the connector and attached one lead to each side.
 
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Old 10-12-12, 01:00 AM
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That is correct. Did you replace the sensor?

Interesting video from hvactech. I've been seeing varying currents for the flame sensing circuit. I saw .7 on one site but I believe that is too low.
 
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Old 10-12-12, 05:29 AM
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Pete,

In general it MUST be more than 1 micro amp for the control to recognize the signal.
 
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Old 10-12-12, 07:00 AM
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I will have a new one today.
 
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Old 10-15-12, 03:33 PM
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Ok just got new flame sensor. I put it in and same thing. I get around 3 uA at start up of the burners (the flame might flicker slightly then stabalizes) and the reading with the new sensor goes to 6.8 uA then I get shut off of the burner. Three times and then lockout. Any ideas what to check next?
 

Last edited by hvactechfw; 10-15-12 at 06:26 PM.
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Old 10-15-12, 06:27 PM
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Sounds like you need a new control board.
 
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Old 10-15-12, 07:39 PM
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I agree with hvactechfw, it's most likely the board, but before you invest in a new board, make absolutely certain you have a good ground.
 
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Old 10-15-12, 08:06 PM
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What is the best way to check for good ground?
 
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Old 10-15-12, 08:46 PM
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You will need an ohm meter or a simple continuity tester.
 
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Old 10-15-12, 09:49 PM
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I have a meter. ground screw on the board to the frame or gas pipe? should give continuity right? I also have continuity ground to neutral.
 

Last edited by joeduck64; 10-15-12 at 10:15 PM.
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Old 10-16-12, 04:14 PM
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Are you getting any voltage between ground & neutral? If not, it sounds like you have a good ground & probably should go ahead & order a board. It's rare but I've seen grounding problems cause the same symptom. I'd rather have you spend a few minutes with a meter than spend $$$ on a board you ended up not needing.
 
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Old 10-16-12, 05:58 PM
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No voltage between Ground and Neutral. Guess I'm ordering a new board, unless anyone has something else for me to check. These board must only last 10 years. I changed one about 10 years ago. Thanks for the help eveyone. I'll let you know what happens.
 
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Old 10-16-12, 06:55 PM
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If your furnace is 20 years old then you need to have the secondary heat exchanger looked at by a professional before you spend any money on your furnace. Bryant/carrier/payne had a lawsuit over failed heat exchangers due to inferior metal used in production.
 
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Old 10-16-12, 08:05 PM
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Would a bad Secondary heat exchanger cause the flame out error 34 and the lockout Error 14? My furnace is 20 years and 5 month old. Would it be covered by the recall? What other symptoms of the bad heat exchanger would I see?
 
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Old 10-16-12, 08:18 PM
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NO, it would not cause those types of errors. If the heat exchanger is failed it may be cost prohibited to put ANY money into that old of a furnace. There was no RECALL. At the age of your furnace it may not be covered by a standard heat exchanger warranty or by the resulting lawsuit settlement agreement. Symptoms of a failed secondary like I have seen on many are: white water marks on or around the blower assembly or blower deck and CO in the home, exhaust gases smell in the home.
 
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Old 10-16-12, 08:51 PM
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But won't it cost me money to have someone come out and look at the secondary heat exchanger also? I'm sure they won't come out for free. I have two CO detectors and neither one has gone off andno exhaust smell. We did have an extremely hot summer and the AC ran alot and there was alot of condensate on the outside of the blower section of the furnace this summer and the drain pipe was almost clogged with rusty deposits. I have cleaned that out. If I get a new board I can get a carrier brand board online for around $200 and I can get a ICM281 board which must be an off brand replacement board for $100. Both have 1 year warranties. Any recommendations on whether the ICM board is a bad idea? I know soon (2-5 years probably) I will need to replace this furnace so I don't want to spend much money on it but I would like to get it working.
 
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Old 10-17-12, 08:42 PM
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Nobody has any advice on the two boards? CES011005702 or ICM281 which are the boards for my furnace.
 
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Old 10-18-12, 02:34 PM
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I've used ICM boards many times. Sometimes there are a few wiring changes but if you follow the instructions, there's nothing wrong with them.
 
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Old 10-18-12, 05:58 PM
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Thanks for the help. I'll let you know how it goes.
 
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Old 10-20-12, 10:38 AM
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I put in the new board last night and the furnace works great. Thanks for all the help.
 
 

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