Starting today, I'm getting an error 31 on my furnace when it tries to answer a call for heat. I gather from reading that this error is typically related to a faulty inducer motor, and indeed I had that same problem last year. I have, however, replaced the inducer and it's been working well since last winter and into the early autumn of this year.

When the unit turns on, the inducer spins freely, starts up quickly, etc., so I don't think that's the problem.

The error states:
Pressure, Draft Safeguard, Auxiliary-Limit (when used, or Blocked vent shutoff (when used) Switch did not close or reopen.

It says to check:

1. Proper venting size and condensation pitch or sag
2. Vent restriction or high winds
3. Defective inducer motor or start capacitor
4. Defective pressure switch or connection
5. Dirty filter or restricted duct system
6. Low inducer voltage
7. Disconnected or obstructed pressure tubing


This is where I'm kind of lost. I'm not sure what the next best (or likely) thing to check is.

Ideas from anyone? Thanks.

 

The first place to start is with the hose that goes between your inducer fan and the pressure switch. Make sure the openings on both ends and the entire length of the hose is clear. Then clean the port on the inducer where this hose attaches. You can clean the hose and the port with a paper clip. Make sure the port is clean all the way to the fan blades inside the inducer.

Check your exhaust vent to make sure there are no obstructions/restrictions such as a bird's nest, dead animals, wasp nest, feathers, and etc.

Make sure all of the vents in your home are open.

Make sure the return air grille(s) is not blocked off by furniture or other object.

Make sure the air filter is clean.

 

Well, it's working now, so I'll thank you for your quick and thorough response. I have a few follow-up questions, since I seem to be spending more time with this furnace than I ever wanted. So far I've been able to find the answers I need, so it's just a matter of putting a tool to the job, so to speak.

From the inducer fan there was only 1 hose, located at the bottom left. It's a fat hose (my pinky fit inside of it) and was only 2" long. It went into the base of the unit, directly above the area where all the circuitry is. Being so large, it seems improbable that it was plugged up, particularly since I didn't find any evidence of that. However, I took it off and repositioned the hose and clips just for good measure.

Attached to the inducer unit there is a round metallic piece that has two small hoses connected. One is labeled "burner enclosure" and the other is labeled "collector box." I likewise took all of those hoses off, blew them out and reconnected, ensuring there were no kinks, etc. My question is, is that latter piece the part that connects to the pressure switch, or perhaps is it the pressure switch itself?

Thanks for the clarification, and thanks again for the excellent help.

 

Glad to hear it is now working. It is important to keep those hoses clear of any restriction/blockage. Here is photo of a unit similar to yours.

Are you talking about the component circled in white in the attached photo?

 

Yes, that was the component I was asking about.

FYI, it's failed again and I think I've narrowed it down to that large, short hose I had mentioned in the previous post. It seems to be a condensation channel and feeds into some PVC line. The hose connecting that is very pliable and it seems that it can get easily kinked. I might have reattached it poorly when I replaced the inducer motor last year and over time it's pinched off. I took that hose off and it seems to work. I'll drop by HD tonight and get some new tubing.

 

Yes, that is the pressure switch. I suggest you make sure the white plastic box with hoses going into is clean and drain piping is clear. Here is a link to some info that may be of assistance to you:
http://www.docs.hvacpartners.com/idc.../58mxa-4si.pdf

Starting on page 4 there is a lot of info about the different hoses and configurations depending on the orientation of the installation such as upflow, downflow, horizontal left, horizontal left and etc. Also good reading on condensate trap and drains.

 

Sadly, it's failing again, so I guess that big hose isn't the issue after all. Bummer.

I'll check the link you provided and make sure everything's cleaned out.

Is the pressure switch a likely culprit, assuming all the hoses are clear? As you suggested, I also checked the filter (even removed it to ensure there was adequate flow) and the intakes - everything looks good.

I guess the confusing part for me is the sometimes works, sometimes doesn't. I suppose I can find a pressure switch and swap that out.

Again, thanks for the help.

 

That white plastic box is the condensate trap. There should be a tube that connects on the underside of it. Need to make sure that is clear all the way to the outside or wherever it drains into. Also, make sure the combustion air intake and vent pipes are clear with no restrictions/obstructions. If that does not correct the problem it would be time to test the pressure switch.

 

I pulled off the line going from the inducer to the condensation trap and about 1 Tbsp of water spilled out from the inducer housing. I'm going to assume that's a bad thing and that it points to the trap and that it's obstructed somewhere between there and the drainage point.

The house is currently 66 degrees which should be fine for the night, so I'll jump on it tomorrow.

Thanks very much for the url of the doc - lots of info in there that's helping it make more sense to me.

 

Here's the update - I pulled the line from the inducer to the condensation trap and fired up the unit. Worked fine for 20 mins or so and just put an absorbent cloth under the inducer's drainage point.

I noticed the blower motor stopped working after awhile and went down to see the status of it. The inducer was still running, but the 31 error was back.

Every time I think I understand what's going on, something happens that perplexes me. I was assuming that there was no positive pressure feedback sensor on the inducer and therefore having the drain just open would be fine. Maybe that's still true. However, I can't figure out why it's still sometimes failing if that's the area of problem.

Would it be worthwhile to simply replace the pressure switch, or am I just completely misunderstanding and the condensation trap is more important than I'm realizing?

 

The pressure switch is the sensor. For it to work properly all hoses have to be connected. Yes, the condensation trap is very important. It must be draining properly. Did you find the hose connection at the bottom of the trap? The drain hose that attaches there must be clear all the way to where it drains. On some systems, the drain traps have to be "primed" so the system will drain properly. Here is a link to another 9200 series manual:

http://www.docs.hvacpartners.com/idc...it/om58-67.pdf

It has additional info about diagnostic code 31.

 

This is almost too much for my financial advisor brain - lol.

I took the condensate trap off and blew it out. All kinds of wet, clumpy, clay-like crud came out of it - see the photo. After having done that, I was feeling pretty confident that I had found the problem, particularly since air easily passed through the trap now. So, I hooked it back up, replaced the line running to the drain and fired it up.


On starting, it faulted with the familiar 31 error. So, I disconnected the inducer from the trap and started it back up. Water spills out and it fires right up. Turn the heater off, reconnect the hose, call for heat - 31 error.

I did this a few more times. Every time I disconnected the inducer, water would spill out but it would fire right up. I even turned off the heater a few times to make certain that I could reproduce. Every time the inducer was disconnected, it worked. Every time it was connected to the condensate trap, it errored with 31.

The trap is sealed, so I can't get a look at what's going on inside, but it seems to mostly be a pass through for the 3 hoses that connect to it. It's working with the other two hoses connected, just not with the inducer connected.

I'm not sure I'll be able to find the trap on a Friday afternoon. Is there a danger/stupidity in connecting a hose to the inducer and running it directly to the drain? Granted, I'm not sure how long the furnace actually works with this current set up or if it eventually faults since I've mostly been focusing on the starting.

 

That is quite a "clog". I think you have more cleaning of hoses to do. The best tool to clean these hose and lines is a shop vac. The trap shouldn't need to be replaced just thoroughly cleaned. Check that hose from the inducer again. If you use a shop vac make sure you don't suck on the pressure switch. The pressure switch may have water in it as well as the inducer. That water needs to come out.

 

The hose from the inducer is clear and short - my pinky can fit in it, so it's very easy to see it's clear.

A few clarifying questions if you don't mind. BTW, I do very much appreciate all the help you've been.

Given that I feel EVERY hose is clear (each has been taken off and I can easily blow through them) I'm kind of leaning toward a problem with the pressure switch. What's the expected behavior for this? I have it off and in my hands right now. Shaking it, I don't hear any liquid in it. If I blow or suck through either of the connectors, I hear a little click inside (sounds like a diaphragm) and the air flow stops after a few seconds - I can't draw or blow any more air through it.

2ndly, related to your statement about water, I assume that water in the inducer is a normal occurrence of the combustion process, which is why they have a drain spot on it. I *am* surprised at the amount of water, though, but it only runs initially when the inducer turns on, the drips while running.

So, clear hoses, clear drainage, clean filter... is it narrowing down any?

 

The hose I would be most most concerned about now would be the hose that attaches to the bottom of the condensate drain. If you look on page 5 of the info I linked in a previous post the top left image shows how the drain hose is connected towards the bottom. That hose needs to be clear all the way to where it drains. If you have already made sure that is clear that is great. You should never suck or blow on the pressure switch as that can damage it. Chances are there is no water in the pressure switch but it is possible. The inducer motor gets moisture in it and that is as you said why they have a drain.. You can test the pressure switch to see if it remains closed with a multimeter.

 

To verify or determine if the pressure switch is what is shutting off the burners connect one multimeter test lead to chassis ground and use the other to check for 24 VAC at the terminals. One side of the pressure switch should have 24 VAC whenever the thermostat calls for heat. The other side of the switch should read 24 VAC on it as soon as the inducer motor comes up to speed.

 

I'll check the voltages on the pressure switch.

Perhaps I should clarify the sequence just in case that exposes anything valuable.

1. Power is off to the furnace; power turned on.
2. After a delay (an excruciating 3 mins) the call for heat is answered and the inducer begins to spin up.
3. The fan seems to get adequate speed and after about 10 secs the light then flashes 31.
4. The inducer continues to spin but will eventually power off (not sure of the timing).

The ignitor never lights, and the burners never come into play, unless of course, it's one of the times when everything's working and it all runs smoothly, as it did this morning. This AM I restored the AC and everything it went through steps 1 - 3, except instead of displaying an error, the ignitor lit and combustion took place.

The furnace ran nicely and stopped after about 20 mins of heating when the thermostats programs were satisfied. After it spun down and turned itself off, I increased the temp on one of the therms and steps 1 - 4 occurred.

 

The guy that installed the unit used PVC glue to attach the drain line to the bottom of the condensate trap, so I can't verify 100% that it's unobstructed, but water and air seem to flow through it without any trouble, so I have to assume it's clear enough for drainage. I completely replaced the PVC line from this one 90-degree elbow down to the drain.

 

The drains are probably clear now. Pressure switches rarely fail but sometimes they do. A problem with the pressure switch is usually an indicator of a problem somewhere else. Yes, you definitely need to verify that the pressure switch is closing and staying closed by testing the voltage as spelled out in an earlier post. The fact that it ran this morning for 20 minutes means that you made some good progress in identifying the problem. As far as the pvc drain pipe I would suggest you put a tee in the piping to facilitate cleaning of the pipe and observe if it is draining. I prefer installing clear hose secured with clamps for that section so you can see if there are any clogs and observe that it is draining properly.

 

I decided to re-read the manual you had supplied and found something that interested me.

On page 6, Figure 8 of http://www.docs.hvacpartners.com/idc.../58mxa-4si.pdf

it shows that the collect box that connects to the pressure switch should have a plug in the end of a tube attached to it. As mine stands, there's just an open port through which a lot of air passes when the inducer motor kicks in. So, I covered it with my thumb and the furnace fired right up. I repeated the process 5 more times to ensure that it wasn't a fluke. With all hoses attached, etc., when I would stopper that port, it worked. The two times I unstopped it, it failed.

Now, I have no idea why it would have worked all this time without being plugged - it's perplexing.

2nd thing, I'm not getting any values on either of the two connections of the pressure switch. Actually, on the rear I do get 0.01 volts when the furnace is off, and 0.00 when it's running. I'm grounding to the chassis, actually to a screw where two other wires connect. On the front contact, I get 0 volts always. So I think I'm not doing that whole thing right.

Anyway, that's what's up. Going to go buy a short hose to stop that port and will report back.

 

Good job finding the missing plug. It does make one wonder how it operated before. Is that the blue with white stripe label hose?

To find out if the pressure switch is at fault, try this:
With your meter set to read ohms and the furnace OFF...disconnect the two wires connected to the pressure switch terminals. Put the meter leads on each one of the two terminals of the switch. The meter should show an infinite readout (open switch). On some digital meters it will read OL or 1 if open.
Set thermostat to call for heat. The inducer blower kicks ON. Meter should now show a reading of "0" ohms (meaning a closed switch).

In other words, with the inducer OFF the contacts of the switch should be open.
The inducer ON should close the pressure switch contacts. They should neither be closed prior to the inducer starting, nor should they stay closed after the inducer stops. And they must remain closed as long as the call for heat continues (and the inducer is up and running)

When the furnace is operating you should get a reading of 24VAC on each terminal of the switch. As I posted earlier, when the inducer starts up, if you place one lead on the terminal and the other to ground you should read 24VAC on the terminal where the power enters. If the pressure switch is closed you will read 24VAC on the other terminal. If the pressure switch is closed the reading ACROSS the terminals the reading will be 0. If the pressure switch is open you will read 24VAC across the two terminals.

You may also run this test live:
1- Turn the thermostat to OFF
2- Disconnect the two wires that connect to the pressure switch terminals
3- Place a jumper wire between terminals W and R at the furnace. This simulates what the thermostat does which is call for heat
4- The inducer blower will kick ON
5- Now connect the two wires you removed from the pressure switch to each other.

If the furnace continues its process and fires as it would normally do, you have a hanging pressure switch.

Pressure switches have contacts that are expected to be in the open position prior to a thermostat call for heat. If the contacts are not open the control board prevents the furnace from firing. After the inducer kicks ON, these contacts are expected to close. If they fail to close same thing, the board will not permit the furnace to fire the main burners.

 

The label on the hose that I have (the one that connects to the condensate trap) is blue, and in reading, it seems that the other one is blue/white. Given that there's a white line around the blue, it's a little confusing to me and I don't know why they just didn't have the second hose be orange or something Of course, I'm sure if I had actually seen both hoses, it would be clear to me which is which. I assume this is the "blue" hose.

The test on the pressure switch showed it closing as you suggested it should, and I'm satisfied that's working fine.

So, having purchased a short length of 5/8" tubing, a few clamps, and a plug, the furnace seems to be working. It no longer seems to need human intervention to get started and to restart.

I now know more about furnaces than I ever thought I would (having placed the inducer and now this work) and I thank you for the wonderful help you extended. I would have been lost without your insight.

 

You are very welcome. Glad to hear you have everything operating properly once again and letting us know the final outcome. It is always a good feeling to tackle a troubleshooting adventure like this and find the solution. Great job!

 

You guys are amazing; great job solving your issue. I just had the same issue with my Carrier 58MVP. Flame went out, but fan kept blowing cold air. Got it serviced, which meant cleaning out the condensate trap. Works now, $225 later. Wish I'd read this forum first. Apparently there was a lawsuit over this issue. Carrier paid out to owners of several models. including mine, but the deadline was 2008. My unit has been working fine, except for rattling, which I now believe was due to backed up water in the system. The service guy said I should replace the pressure switch and trap, and the blower if it was damaged due to corrosion. Another guy advised me to do nothing unless something else goes wrong.

I plan to reconfigure the drainage hose and keep an eye on the trap, cleaning it regularly. I've always kept the air filter clean. Do you have a diagram to show how to properly configure the drainage? It goes into a floor drain, uses clear hose with grey elbows or tees where needed (the humidifier drains into the same place), but the hose coming from the trap is partly collapsed and water sits in that section where it sags a bit. Should there be a trap in the line before it hits the drain?

 

No, you shouldn't need an additional condensate trap other than the one already installed. There is no diagram for a condensate drain as every system's layout is different and needs to be configured accordingly for proper drainage. Code requirement is 1/4" pitch for each 1' length of pipe. In other words, if the drain pipe is 4' long you would need 1" of slope. You definitely do not want any sags in the drain hose. Sags prevent proper condensate drainage.

 

I found this thread after getting similar symptoms as the OP. And disconnecting the hose from the burner enclosure to the pressure switch lets the furnace operate for a while before it shuts down.

I disconnected the pressure switch, shook it, and unlike the OP, mines full of water. I'm in Milwaukee and today's actually a good day for the furnace failure - it's going to hit 30 deg instead of reaching lows of -7 to -17 for the last few weeks.

Back in November, I originally fixed the error 31 problem by reading all your posts. The problem was a plugged condensate trap. About a quart of water came out of the burner enclosure drain. I'm sure the water got into the pressure switch then which chugged along till now.

Just posting this to say thank you to everyone here for helping out the OP and secondarily me. I didn't even bother to electrically test the pressure switch. When I heard the water sloshing, I just assumed it's bad and ordered the new one. Right? I've got the switch wires shorted and the furnace is working until the new one arrives.

 

Well this is interesting. Nearly a year to the day since I first posted, I fired up the ol' Carrier and got the same 31 error. As a side note, I found this thread again, failing to remember that I was indeed "ChillyBilly" since my name has nothing to do with Bill or William, etc. I *was* amazed at the OP and how it mirrored what I experienced, and even how Bill's "voice" sounded like mine. Ha!

Anyway, all the lines checked clear and there was just a bit of water in the condensate trap - everything looked fine.

I put a VOM on the pressure switch and never got the igniter firing. I decided to short the switch [btw, please tell me if I'm doing something that will lead me to blow up my family!] and it fired up.

I removed the short and everything kept running. The switch showed it had closed (via the VOM) and there was 24 VAC on each terminal.

Note to the noobs (of which I am one), it seems before the inducer motor runs there is a check to ensure that the switch is open. If that checks out, it'll spin.

So, having turned everything off and restoring everything to its rightful place, I turned it on and initiated another call for heat. Sure enough, this time, it worked as would be expected.

Now, I haven't done multiple starts to see if it's really going to work. Wondering, though, would it seem reasonable to think that the switch wasn't closing for whatever reason (maybe worn, stuck, etc) but once the system operated normally (with a little help) it cleared that sitch up? [not switch, sitch, as in situation].

Anyway, kind of feeling like I should just pop a new pressure switch in the old girl.

As always, comments and ideas are welcomed and appreciated.

 

When a furnace sits idle for several months some of the components tend to "clog" up slightly such as the condensate trap/drains, inducer motor, pressure switch hose(s) and etc. You are correct that the pressure switch needs to be open before the inducer will start. This is a safety feature to prevent firing of the furnace if a condition is present such as a blocked vent pipe. By jumping the pressure switch and getting the inducer to start you probably cleared out a slight blockage in the system. Pressure switches very rarely fail and do their job. I suggest you continue to keep an eye on operation of the system and it should be fine. As always, basic maintenance should be performed on a regular basis.

 

Well this seems suspicious to me. It's a rigid plastic in the burner side connection. It broke off but there's still residual somethingorother in there.

 

I don't usually post in these forums. But this thread was a lifesaver. It was -17 below zero last night. Not supposed to be as cold tonight, but we came back from a trip to find our house at about 55 degrees and the furnace wasn't running. I did everything I knew how and couldn't get it to stay lit. It would light the burners and as soon as the blower would turn on, the gas to the burner would cut and they would go out. It took me a while to figure out how to find and read the LED error light and I learned it was a 31 error. But none of the suggested fixes made sense. This thread showed me to start looking at the drainage hoses on the inducer fan.

I still can't tell if or where I have a clog, but, there is a ribbed hose coming off the back/bottom of the fan assembly. The hose is about 3/4" to 1" in diameter. I removed that hose from where it hooked to a white plastic housing that goes down inside the metal housing of the furnace. Water just started pouring out of the hose. I grabbed a bucket and probably caught a pint of water. I don't know how much went onto the floor before I got a bucket. Anyway, there was a lot of water in there - I guess up inside that fan housing? I don't know where it came from.

I undid the the small house - about 1/4" - and there was just a drop or two in that hose. I then undid the metal panel at the bottom of the furnace to see where the white housing went. I could see the drain hose that ran from the bottom of the white plastic out of the furnace cabinet/housing to the drain in the floor. I undid this just to see if any more water would run out. None did.

I put everything back and turned the power back on to the furnace. It started up like it had been doing, the burners lit up, and they kept going!

Thank you for all of the advice. My kids will be warm tonight.