Hi,
I have a Carrier 90+ Furnace model 58MCB that is 1 year old ( Heat only no AC installed ). It has been a great furnace up until today. I came home from work and it was cool in the house ( 60 degrees ). The furnace had been working flawless until today. I have a Honeywell thermostat that allows me to lower the heat automatically while I am at work. It is set at 55 degrees while I'm at work and 68 degrees while I am home. Today it isn't heating up. I checked the thermostat and it shows the flame to show the furnace should be on. But the furnace wasn't on and didn't come on in 10 minutes.
I manually turned the thermostat down and waited for the indicator to go off. I heard the thermostat click off. I then turned the thermostat back up and the indicator clicked back on. The burner fan on the furnace kicked on and ran for a minute or 2 then turned off.
I pulled the front panel off and noticed the red LED troubleshooting light blinking. It was blinking 3 times, pause then once ( I am assuming code "31" ). I disconnected the power to the furnace for about 15 minutes and then plugged it back in. The furnace cycled just like it did when it was first installed ( main fan run for a minute, then turned off, then the burner fan turned on for a minute ). How ever that is all that has happened. Currently it isn't heating at all.
What is code 31? Are there any common failers on the model furnace? Any thing I should check or could check? I am very mechanicaly inclined and am not afraid to attempt a fix ( if I have a idea what might be the problem ). Can anyone point me in the right direction?
Thanks in Advance.
Bob

p.s. I'm a machinest by trade, but also I work on cars, trucks, atv's, ect. Basically there isn't much I don't work on. I'm not a know it all, i just love know how things work and I like fixing things.

 

Usually you will find an explanation for the diagnostic codes on the inside of the fan compartment cover. Typically the Carrier 3-1 diagnostic code is displayed when the pressure switch fails to close.

The inducer motor is the "burner fan," which should switch on whenever the thermostat is calling for heat, and which produces a negative pressure that pulls the air and combustion gasses through the furnaces and into the venting system.

To verify that this system is working properly, the pressure switch checks to see that an adequate negative pressure is developed. If it isn't, the burners are not turned on.

So you probably have a defect in that system of air being drawn through the furnace and venting system. Don't bother replacing the pressure switch, which is a problem perhaps 2% of the time.

But check EVERYTHING else for possible plugging. A leaf drawn into the fresh air inlet pipe is a common source of such a problem, as are sags in the PVC piping which allow water to puddle or a plugged drainage system for the water produced by burning the gas, plugged sampling ports or plugged rubber tubing to the pressure switch.

Because there are a lot of rather subtle things that can cause this defect, you may or may not be able to identify the cause. Good luck.

 

I turned the thermostat up and got the inducer motor running and went outside quickly to check if there was any air flow. There seems to be quite a good flow of suction and blow out from the pipes. Check

I then searched and found the trouble codes on the back side of the front panel. I have taken this panel off a few times before but never noticed this sticker. I then went through and double checked everything on the list.
The last think on the list was "bad pressure switch". I then looked at the switch and thought to myself: I wonder if one of the lines are some how plugged. I unplugged the one line and blew through it lightly just to see if it was plugged at all. It seemed slightly restricted but opened up quickly. I then hooked it back up turned the furnace back on and turned up the thermostat. the furnace cycled like normal start up ( main fan on, then off and then the inducer fan started. 30 seconds later the burners kicked on and wa-la heat!!!!!!!!!!!!!!!

I can not begin to say how Thankful I am to you for pointing me in the correct path of checking and then figuring it out.

Thank You!!, Thank You!!, Thank You!!, Thank You!!!!
I was getting really worried ( and chilled ) here. They are forecasting temps of 20-25 tonight I really need the heat on.

 

Thanks for the post I happened to have the same issue as 4howdy, checked the intake and juggled and tapped all the hoses and she started working again! Saved me a $300 emergency repair bill.

 

Thanks!!!!!! I ran into the same problem and blew both of the small hoses connected to the pressure switch. of couse I wouldn't know which one was the problem now, but I got heat now and it's -30c outside...

 

I had same problem, checked the intake and outflow pipes and found good flow. Disconnected the small tubes connected to the pressure relief switch, blew into them and reconnected. Turned furnace back on and got heat! thanks

 

First off I read up on this 58mcb model which I bought new and helped install in an older home .It sees a lot of people are very unhappy with theirs after a short time and service calls parts etc .

Here is how mine acted before it stopped working and the power went out a day before ..the 2 fans would work when I turned up thermostat but no heat and it was flashing a code 3 short blinks then one long .. I tried turning off the breaker , turned off the the gas supply . and pressing the reset button for the ignitor and waiting for 15 minutes as suggested in owners manual ..I also tryed blowing in the small vacume lines and checking the vent intake and exaust pipes for blockage as well as the condensate water drain.. I even tapped on the gas thermocouple box thingie with a wrench ..well dont know for sure what the prob was but it is working again now so this thread is usefull it does not throw any codes now the red led stays on and is heating the house and running its cool down cycles as it should .. thats my 2 cents worth hope it helps

 

my first attempt only partially worked it started throwing the code again ,,so I tried some different thing I took of the cover and ran the jumper yest as the book and panel sticker explain and everything went thru its cycle ..then U pulled apart the water resevoir and fond a lot of water still in it so drained that ...I also pulled out the air filter which was pretty loaded up ..well now its ran thru several cycles with no further problem but im watching it closely because winter in alberta is just around the corner I hope its ok now but am not confident after all the bad i have heard about this furnace ,,I will re post any future developments Im not a pro but have no money th throw at this thing as far as getting the quy back out here ..I need to know how to fix it my self and I willl by trial and error ..next thing I will try if it stumbles again is the flame sensor in the burner box I will try cleaning it ...good luck out there I like the concept of sharing info thats why im here ! Leon

 

OK, I've got the same problem with the same furnace model and it is 8 years old. It has happened in the past and it's always the first winter blast when you needed the most. The previous years, starting procedure described in the manual did help so it was easy to restart after the failure with the "31" LED code. Today I got lost, it did start in the beginning and it worked a couple of hours and then it died with code 31 up to the present time. I tried all of the suggested ideas about the hoses but I think that is not the reason. The code error 31 reffers to the pressure switch and it is true why the LED flashes that code. I checked with an Ohm meter and the switch stays open. I checked the switch with blowing into it and it closes with the lightest effort to blow into the upper rubber hose. I have the same furnace (a working one) on the second floor and I compared, both switches are closing very easily so I removed the swithch from the list of problems. I have temporarily bridged the pressure switch with the multimeter and the current was about 160 mA. The activating of the switch circuit forcely made the burner to glow in bright red which did not happen before but still there was no ignition and the control board shot down everything for safety reason. My last option is that I have defective gas valve because there was no ignition but nobody ever mentioned such possibility with error code 31 before. The voltage to the gas valve is good (around 14 V) the same as the good working furnace upstairs. I have yet to open the gas valve to see if the coils are activating and opening the dual valves built in.
Has anyone had any thoughts about the gas valve causing this since such possibility was mentioned in the manual as insufficient gas pressure? Thanks for any input.

 

Welcome to the forum!! Have you tried removing the pressure switch from the working furnace and installing it in the non-working one to see if that corrects the problem? Pressure switches rarely fail even though it is quickly replaced. You stated you had tried all of the suggested ideas about the hoses. Did you inspect the hoses to make sure there are no cracks/holes and they are clear all the way through. Also, did you make sure the nipple where the pressure switch hose attaches is clear all the way through? Over time the small hole in that nipple will clog up with crud and prevent enough vacuum to close the pressure switch. You can use a small drill bit or opened paper clip to ream out the nipple making sure it is open all the way through. This sometimes takes some effort and often times people fail to get it open all the way through.

Did you make sure the intake and vent pipes are not blocked by a bird's nest, bee hive or some other object? Also, make sure the condensate drain system and trap are completely clear. A restriction/blockage anywhere in the condensate drain system will cause code 31.

 

Thanks for the tips. It turns out it was still all about the pressure problem. It wasn't the switch itself or any clogged pipe. It was the counter air draft coming from the exhausting vent. There was no significant wind to make me to suspect that option but when I removed the connection from the inducer motor that takes the exhausted air out, the furnace started right away. However it did stop a few more times but every time I disconnect the exhausting pipe it starts without hesitation. I tried to put an elbow on the exhausting pipe outside of the house and turned it to different directions but there was always cold air draft coming from outside that was preventing the furnace to start. I am thinking maybe the motor/fan itself has lost some of the sucking power or some other detail that reduces its power but it is clear now that the air pressure was the problem all the time. I was thinking about putting a small additional fan on the exhaust to help with the air outtake but I know it wouldn't last because of the vapors in the exhausting air. I got heating right now and I know it's going to happen again with this bitter cold weather as it is in Denver right now but at least I know where to look to improve the situation. Thanks again.

 

Glad to hear you figured it out and restored heat. Wind can definitely cause issues with the pressure switch operation. Here is a link to the installation manual for your furnace. It has a lot of good information about the piping and terminations: http://www.havenhomeclimatecare.ca/w...e-90-58mcb.pdf

There are charts in the manual that show maximum allowable length of pipes and required diameters.

 

I do have a installation/user manual but this one is more detailed and includes the wiring diagram too, it looks great. Thank you.

 

You are welcome! It is good to have every bit of information available when working on these systems.