How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site. Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask BillyHvac Your Own Question
BillyHvac, Journeyman HVAC Tech
Category: HVAC
Satisfied Customers: 22634
Experience:  Endorsed for unlimited heating, cooling, oil burners, boilers, refrigeration, hydronics
Type Your HVAC Question Here...
BillyHvac is online now
A new question is answered every 9 seconds

My Bryant furnace keeps shutting off. What could be wrong?

This answer was rated:

My Bryant (Carrier) Plus 90 furnace, model 398AAW036080D shuts off after running for a bit. I can reset and it will come back on, but always shuts back off, so I assume it is sensing a problem during safety checks. I checked rubber hoses going to pressure switch for clogging, nothing there really but blew them out anyway since I had that problem before on another furnace after creating a lot of dust in my basement where it was located. Same scenario this time with dust and basement, but this furnace draws air from outside for draft inducer (I did visual check and didn't see anything stuck in pipe, but I didn't shake it out or anything), where as the other furnace got air from the basement. Also, water is leaking from under draft inducer motor once blower kicks in to send hot air through ducts. I can't tell where it is coming from but I think the condensate pan is behind the motor. So, perhaps the water is touching something that causes the furnace to shut down? To investigate further I took the bottom door off and pressed in the safety switch with the power on. When I did this I saw an "arcing light" come from the electrical control box, not sure what it was but the source of the arc came from a small plastic box with clear top located in a larger metal box containing a control board and other items. The furnace ran fine after the arc and then shut down after running for about five or ten minutes like every other time with this problem.

So once the furnace shuts will not restart on its own?

Customer: replied 6 years ago.

It will if I turn it off at the unit and at the thermostat, which I assume resets it. Wait about ten minutes and turn them both back on. Otherwise, the thermostat will read "Heat on" but nothing will be happening.

Does your spark cable come from a small 2"x3" box or a 3"x5" box labeled lockout timer?
Customer: replied 6 years ago.

I am at work and can't look, but if you can provide a link to a diagram or picture, I might be able to tell. Sorry, I meant to take a picture with phone for reference. The only boxes I can recall are made of sheet metal: a small one about 2x3 to the right of the inducer motor that has the pressure switch attached to it and says it has hot wires and to not service without turning power off and the other is behind the lower panel and is about 3x5 and has the control panel and some relays or something in it. I haven't investigated into the inside of either box yet. I was hoping the lower box would have a troubleshooting mechanism in it. My old York Diamond 90 (in another house) furnace had a blinking red light for such purposes. BTW, I don't know what a spark cable looks like either.

Carrier Lockout Relay Timer P/N HH72CH003 - Click Image to Close

The cable runs from the pilot and is orange.

I will leave this open for you for when you are at the unit

Customer: replied 6 years ago.

Orange wire going from burner box to a 2x3 black box labeled spark ignitor (doesn't look like picture). Blue and green wire going from that box to where gas is turned on or off.

Btw, turned it on and it ran normal - long enough to bring temp up from 62 to 66 then shut off. Thermostat was set at 74.

Thank you.

Do you mind a hands on test?

Remove thermostat, take wire from R and wire from W (usually red and white and twist together. Time how long furnace runs before shutting down.

Customer: replied 6 years ago.
Ok, twisted and running now. Timing in progress, is there a point where I would stop if it doesn't?

Tell me when it has run longer than normal...or if it doesn't turn off. I am looking to see if it runs without shutting down as it did before.

Once it either know it has already ran longer than before let me know.

Customer: replied 6 years ago.
Flame went out at 12 minutes, fan went off two minutes later.

Thank you...and the wires are still twisted together?

And it ran longer than before?

Customer: replied 6 years ago.
About the same run time, if longer it was not much, and yes wires still twisted. FYI, the first couple of times the original problem happened, I could reset it and it might operate normally for hours before shutting off again. Now it's only minutes.

Ok...we are getting there..

When flame shuts off...does the exhaust fan shut off just before, same time or after?

Customer: replied 6 years ago.
Two minutes after on the test we ran, not sure any other time because I'm always away from the unit.

And finally.....the main blower that sends air through the shuts off when?

Customer: replied 6 years ago.
Sorry, but I'm not totally sure if what stayed on two minutes longer was exhaust fan or blower or both. I thought it was blower first, but since you said exhaust fan I went with that without explaining. I can test again if it's critical to distinguish between them.

Sorry...but it is important.

Format as such:

Exhaust starts

Pilot lights

Burners fire up

Flames turn off 10 minutes later

Exhaust turns off 2 minutes later

Main blower turns off 1 minute later

Customer: replied 6 years ago.

Forgot to turn unit off to reset from before, so will take some time to start test.

Second test - Draft inducer came on with pilot, but flame never kicked in before shutting down. Resetting for another test.

Third test - Power on, exhaust starts, pilot lights, flame and blower kick on, all happened within 1.5 minutes. Ran for 5 minutes, then flame went out but blower and exhaust both stayed on for another 2 or 3 minutes. Same as first test it seems, except didn't run as long.

Thank you.

This is sounding like the 3 wire pilot is going bad. The pilot has a warp switch in the side of it. It lights, then it heats up the side warp switch...after a while it warps and connects and sends power to the gas valve for main gas.

I am also suspecting a "domino" theory that the small circuit board behind the pressure switch is affected.

From your last said flame goes out...but what about pilot?

Customer: replied 6 years ago.

Pilot and flame out at same time.

The pilot will need to be replaced first.

This is what is holding the unit pilot mode. Change pilot and let me know.

Customer: replied 6 years ago.
Will do, thanks!
Customer: replied 6 years ago.
Just replaced pilot, everything ran like normal so I lowered thermostat until it no longer called for heat, flame went out and blower and exhaust fan stayed on for about two more minutes. I raised thermostat to about ten degrees higher, but furnace never did anything. So, back to the drawing board. Supply house said I was starting at right place with pilot, so now where do I go?

Did you say the inducer motor runs after the flame and pilot go out...or at the same time.

Customer: replied 6 years ago.
I think it stays on after flame and cuts off with blower, but I am not sure. Is there an easy check?

Now that I am confident the pilot warp switch is sending power, I now need to access the inducer relay board (behind the pressure switch). The key now is if the pilot and flame go with the draft motor or if the draft motor continues to run after the pilot/flame goes out. Sorry but to find out means babysitting the unit and seeing what happens at shut down.

Customer: replied 6 years ago.

Ok, resetting now, so have to wait unless you know a quick/immediate reset.

Btw, if I turn power on at unit before enough time has elapsed, I hear a click at the relay board you mention. If enough time has passed, unit starts normally.

Draft motor definitely stopped at same time as when flame and pilot went out. Blower continued for two more minutes.

Small circuit board behind pressure switch controls the inducer motor. Is there a chance the motor faults and in a split second the flame goes with it?

Any faulting of the inducer will be because of that small board. Look at the back of board for hot spot.

Customer: replied 6 years ago.

Ok, thanks. I might not be able to check until tomorrow.

I looked at it last night, but of course I only looked at the front. If I don't see anything on the back, is there a next step?

Not sure about faulting, but motor seems to work ok while running (it puts out a strong exhaust) and I felt it after it shut off and it wasn't overly warm or anything.

This was one of the designs that were tried and stopped real soon after. The small circuit board had a very high failure rate. It can cut the inducer at will...and also not start up unit.

Quite often there is a brown spot on the back of the board. I want you to check first instead of building a new furnace part by part....

Customer: replied 6 years ago.

No brown spot, looks perfect, all solder joint intact; best I can tell.

Thank you.

At this point we need to see if the main board is dropping signal to the inducer board or if inducer board is dropping signal back to main. Do you have a volt meter?

Customer: replied 6 years ago.
No but if it's the only way I can borrow one.


To save time I am going to format a troubleshoot...terminal to terminal and send. Will pull the schematic and give you a course of action with what to do depending on results.

Customer: replied 6 years ago.

Awesome, thanks. I'll tackle it this evening or over the weekend. BTW, I realize this has gone on now for a week and I appreciate your patience ... also, we don't need heat at the moment, temps have been moderate so it's afforded me the time to tinker. Now, if work didn't get in the way, I'm sure things would have moved faster.

Coming from the pressure switch are 3 wires...yellow, orange and brown.

Orange is our 24V to the pressure switch from the board (small one behind pressure switch). We want to put one meter lead to orange and one to ground. We need 24V on the orange all the time after start up. To start, 24V connects to yellow....once the pressure switch closes it connects orange to brown.

Once brown gets 24V from the orange at pressure switch it enables pilot.

It does this by connecting through the edge connectors. Pull edge connectors and use a flat piece of sand paper and clean contacts.

If you can, clip meter lead to any ground on cabinet and then to the orange wire on pressure switch.

If it faults and there is no 24V on orange = replace circuit board in blower section or check edge connector.

If 24V remains on orange, replace small circuit board behind pressure switch.

Customer: replied 6 years ago.

Tested four times, each time the volt meter read around 26.8 after the flame went out and blower and fan shut down. So, will replace small circuit board behind pressure switch according to steps above and let you know the outcome.

I will wait for your reply.

Customer: replied 6 years ago.

Success! Evidently, that inducer board was upgraded in 1989, so pretty long run for the substandard old one. Had to add a red wire from limit switch to board, but otherwise easy install. Thanks for all your help.

I am very glad it came to an end for you!

Bet you know more about your furnace than you ever thought you would...Smile

Thanks for all your patience with me. I do this between my regular job and home and realize I am not always quick with showed great character....thank you!

BillyHvac and 2 other HVAC Specialists are ready to help you
Customer: replied 6 years ago.
You were great, thanks!