# Bryant Plus 90 Furnace - Error Code 31



## steve8091 (Oct 4, 2016)

Hi everyone,

I'm glad to find these forums; after doing a little bit of work and a lot of searching, I thought it was time to seek out some specific advice for my problem. The cold weather is coming, and the furnace isn't working. When I tried to start it up, the fan will run, but I get no flame, and thus the fan shuts off after a 90 second delay. It is throwing a code 31, which is related to the pressure switch. Let me tell you what I know and what I've done thus far.

Over the summer, an air filter that was put in a bit crooked got partially sucked into the blower, and the debris was spit out into the condensate drain lines, clogging them up. I discovered this and cleaned everything out from the drain lines on, and it was back up and working again. In the meantime, however, I suspect that components inside of the furnace may have seen some water damage.

I started by doing all of the REALLY obvious stuff (thermostat setting, filters, intake pipes outside the house, etc.).

I then did a few recommended 'tips and tricks' I found online, including hitting reset switches, tapping on the pressure switch, blowing gently to ensure it was engaging, and the like. Unfortunately this didn't help.

The pressure switch sounded a bit strange to me, as if it the diaphragm had a tear, so I ended up replacing it, but to no effect.

I also disconnected the lines leading outside of the house, and drained out quite a bit of what I believe was condensate that formed in the warmer months. I was encouraged to find this, but still nothing.

One point of note (not sure if this is important), but the blower can be installed in several different orientations, and thus has multiple drain ports. One of those ports is covered by a rubber plug, and that plug has deteriorated and has a tear in it. It doesn't feel like much of anything is coming out of that port, but I wasn't sure if that was an issue.

I went so far as to temporarily jumper the pressure switch (yes, I realize that this wasn't the safest move), which is where this gets interesting. After doing this, I smelled gas, and quickly shut everything down. This almost makes me think that the igniter is bad, but I'm not confident in that.

I believe my next step is going to be to replace the igniter, but any insight that you all can provide, given what has happened to this furnace specifically, would be greatly appreciated.

Steve


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## roughneck (Nov 28, 2014)

Check the exhaust for blockages.


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## user_12345a (Nov 23, 2014)

a competent tech with a manometer could figure this out quick.

there's a reason why the pressure switch isn't closing, it's not defective.

Could be many things -> failing inducer, blocked secondary heat exchanger (carrier/bryant used to use a secondary with a plastic coating, he coating can fail and cause blockages, corrosion), blocked condensate lines/trap, badly cracked primary heat exchanger, etc etc.


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## supers05 (May 23, 2015)

Do you have an electrical multimeter? Preferably with an amp probe? 

You can shut off the gas at the valve, then try what you did again. (The circular knob on the gas valve inside the furnace, this is very important.) Wait the ignitor to start to glow. If it a spark type ignore below. 
If it doesn't glow let us know. If it does, and you have an amp probe, clamp it around One of the wires to the ignitor. Report the number when it's the brightest. 

Pictures and model number will help. 

Cheers!


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## steve8091 (Oct 4, 2016)

Brilliant! I figure that it has to be something in the ignition circuit itself, as shorting the pressure switch enabled gas to flow, but no flame. I do know my way around a multimeter, as I repair arcade games as a hobby. I will try this tonight. Many thanks!!



supers05 said:


> You can shut off the gas at the valve, then try what you did again. (The circular knob on the gas valve inside the furnace, this is very important.) Wait the ignitor to start to glow. If it a spark type ignore below.
> If it doesn't glow let us know. If it does, and you have an amp probe, clamp it around One of the wires to the ignitor. Report the number when it's the brightest.
> 
> Pictures and model number will help.
> ...


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## steve8091 (Oct 4, 2016)

I can't figure out how to edit my previous post, but as I think more about it, I must have a compound problem. The pressure switch doesn't make, so there is an issue with adequate pressure flowing across it. On top of that, when I short it, I get gas but no flame. I'm going to go ahead and troubleshoot the igniter as was suggested, but I've also got to figure out what's going on with the pressure.

I realize that there are many things that could be going on, but I wonder if the condensate backup has a tendency to fail any particular components that I could start investigating. Further, I think that I've already cleared out obstructions from the exhaust (there was water there as I mentioned, and I checked the line outside for obstructions), but I'm not confident that I've looked far enough upstream in the furnace itself, beyond the exhaust pipe connection.


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## steve8091 (Oct 4, 2016)

Alright, so I had some time to look more closely tonight, and I'm afraid I jumped the gun quite a bit. The inducer motor isn't running.

I checked the thermostat, and the board on the furnace is indeed showing ~24 VAC when calling for heat. As near as I can tell, however, the board isn't sending 120V to the induction motor. I'm not 100% confident that I'm testing it properly, as there aren't any clear terminals to hook up to.

What I did (see attached photo) is disconnect the 3-wire harness to the motor and tested the incoming wires, both W/G and B/G, and got virtually zero voltage. Interestingly, I did get a very low voltage on one of the two, a definite move from zero, but extremely small (less than 1V). So from this, I'm thinking that I have a bad board. Looking at the board, it looks pretty darn corroded, too (see photo), although perhaps this is typical of furnaces. It seems like this could have been a result of the condensate flooding I had over the summer. Any thoughts are greatly appreciated!


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## user_12345a (Nov 23, 2014)

jumper r and w straight at the board. check voltage from w to c with door switch depressed.

power to the board, both 120v and 24 v, call for heat and no power to the inducer indicates a bad board. check for inducer power at the connector at the board, not at the inducer to rule out wires/connectors.

jumping out the pressure switch could have been very dangerous, the furnace could have fired without the inducer on. you're very lucky that it didn't.


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## steve8091 (Oct 4, 2016)

I checked the board to confirm that the harness connections were okay, and they were - I still get very low voltage. Interestingly, I definitely get 1.0 VAC when I power up, which then tapers to 0.6 VAC over the course of a few seconds, and it holds there. I assume that this is an artifact of the board logic, but it's definitely a far cry from the 120 VAC it should be. Time to order up a replacement board. Thank you all for the help thus far. I'll report back when I know more.


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## supers05 (May 23, 2015)

steve8091 said:


> I checked the board to confirm that the harness connections were okay, and they were - I still get very low voltage. Interestingly, I definitely get 1.0 VAC when I power up, which then tapers to 0.6 VAC over the course of a few seconds, and it holds there. I assume that this is an artifact of the board logic, but it's definitely a far cry from the 120 VAC it should be. Time to order up a replacement board. Thank you all for the help thus far. I'll report back when I know more.


That board definitely got wet and is toast. 

Once you replace it, leave the gas off. Let the furnace go through a ignition attempt. Watch for the venter motor to spin up. The ignitor glow. Then the distinct click of the gas valve. If this all happens, then it's time to try it with gas. 

Cheers!


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## steve8091 (Oct 4, 2016)

Well my friends, I am pleased to announce that my replacement board arrived today, I swapped it in, and I am back up and running! Many thanks for all of your help!


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## supers05 (May 23, 2015)

steve8091 said:


> Well my friends, I am pleased to announce that my replacement board arrived today, I swapped it in, and I am back up and running! Many thanks for all of your help!


I'm happy to hear that you got it working. 

Cheers!


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