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Appliance Man
Appliance Man, Home Appliance Technician
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How to fix error code F31 on a Maytag Bravos dryer?

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Maytag Bravos dryer model MEDB850WQ0, error code F31. Diagnostic says I'm only getting 120 vAC but I measured 220+ at the outlet and where the cord attaches in the dryer. I've replaced the thermal fuse, thermal cut-off, thermistor, and control board. I've visually inspected the heating element. The problem persists and I'm stumped.

I just looked up the tech sheet and f31 is a code that only deals with line voltage. Test where the cord connects to the dryer. Test the outside wire to the outside wire. What is your reading? Test the middle wire to one outside wire. What is your reading? Yes the other outside wire to the middle. What is your reading?

Customer: replied 4 years ago.

Outside to outside toggles between 246 & 247. Both the left and the right outside to middle toggle between 122 and 123.

Ok now access the control board and test the red wire on the heater relay to the middle wire where the cord connects to the dryer. What reading do you get?
Customer: replied 4 years ago.

I get zero on the red. I also tested the black to middle and am getting 120.

Ok you are not getting l2 to the control board. You either have a bad heating element, high limit thermostat or thermal cutoff. Looks like you replace the cutoff so I would check the high limit thermostat. It is located on the side of heater canister. If that is closed then check the element for continuity.

Customer: replied 4 years ago.

I've inspected the heating element and it looks fine. The thermostat was the one part I was having trouble finding in stock so that's no doubt the bad part (Murphy's Law).

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Customer: replied 4 years ago.

Just realized I'm not sure how to check the thermostat. It has 3 connectors, 2 large gauge (red and black) connectors and a small harness connector. I get continuity between the large connector prongs but I'm not sure how to test for open. Can you walk me through what I should be checking?

On my wiring diagram it shows only 2 wires a black wire to a red wire with a white stripe.

Customer: replied 4 years ago.

There's a small collar around the thermostat with a connector for a small harness and what looks like a probe. This link will take you to some photos...

https://w ww.google.com/search?q=whirlpool+8557403&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a&um=1&ie=UTF-8&hl=en&tbm=isch&source=og&sa=N&tab=wi&ei=quEfUcf5CvP7yAGAjoGgDA&biw=1393&bih=876&sei=rOEfUf6SG4qxygGh4YDIAg

That link didn't work. It should look like this. CLICK HERE
Customer: replied 4 years ago.

Yes it does. I get continuity between the large connectors but what other tests should I run?

Then that is good. Did you replace these parts?

CLICK HERE

Customer: replied 4 years ago.

I replaced the part on the right but although I have a new one, I don't see the part on the left anywhere in the dryer. Any idea where it's located?

You need to replace both of them. I believe that one is on the exhaust housing and the other is on the heater canister.
Customer: replied 4 years ago.

I've examined the unit from top to bottom and this part (#3391914) is nowhere to be found nor is in the parts list for the unit. Could that collar on part #8557403 serve the same function?

It might. I would replace the high limit thermostat.
Customer: replied 4 years ago.

Replaced the thermostat but there's no improvement.

The only other part L2 goes through is the motor.
Customer: replied 4 years ago.

Since I'm sure that's not an inexpensive part, though none of them have been so far, is there any way to positively determine that the motor is the source of the fault? And can that be done while it's all disassembled so I have access to it?

The only things you can do are start following the red wire from the terminal block and see where you lose the 110 volts.

Customer: replied 4 years ago.

What state does the dryer need to in while I'm doing this? If it need to be running I won't have access to very much of the wiring. Can I do this with the drum removed?

Customer: replied 4 years ago.

With the front off and the drum out I can verify the motor is receiving 125 but I can't verify its outputting 125 because I can't start it.

Customer: replied 4 years ago.

I'd sure prefer to fix the 2.5 year old dryer instead of buying a new one.

Can you reread the voltages and tell me what you get for a reading?

Customer: replied 4 years ago.

Please tell me which read points you're interested in and I'll get the measurements to best of my ability.

Where the cord attaches to the dryer is what I am wondering. Read the left to center and then the right to center and then left to right.

Customer: replied 4 years ago.

The last readings I took were 122/123 from each side to center and then 244/245 from side to side.

Okay and that was at the dryer? Also, does the dryer come on at all?

Customer: replied 4 years ago.

Everything seems to work EXCEPT the heat.

Okay, you have a voltmeter obviously. With the circuit breaker off to the dryer, gain access to the heating element and disconnect the 2 wires going in to the heating element. Then connect your meter to the 2 wires and now turn the dryer back on and see if you get 220vac. If so then you have a bad heating element, if not then what does the voltage read? Also, if you checked the thermistor what reading in ohms did you get?
Customer: replied 4 years ago.

This is where I get stuck, to gain access to any of the heating system I have to remove the drum. Once I've removed the drum there seems to be switches that prevent the motor from running, the heat coming on, etc. I'm guessing there's a test fixture of some sort that inserts between the main harness and the motor that allows for testing the rest of the system. I don't have one of those so I don't seem able to rout power throughout the system.

I understand now and now I need you to do 2 things. Since you will have to take it apart and will have no power then go ahead and check the resistance on the thermistor (if you haven't replaced it yet) and still disconnect the wires to the heating element but now check for continuity on the heating element itself. Sometimes they may look good but will still be bad.
One other thing have you tried the dryer in any other heated mode. Does it do it in only auto mode or does it do it in auto and timed dry mode?
Customer: replied 4 years ago.

Yes, we tried it in several modes; all without any sign of heat.

Customer: replied 4 years ago.

I'm seeing .4/.5 ohms of resistance on the thermistor and I have continuity on the heating element.

Okay, is this what you are calling the thermistor?

Thermistor(###) ###-####        Main Product View
If not I need you to look at the diagram I am sending you and test 2 parts. The first one is #41 (thermal fuse) and the second is #51 (thermistor). I need a resistance check on each and as you can see they are on the blower housing.

Customer: replied 4 years ago.

Okay, thermistor p/n (###) ###-####measures 12.6k ohms of resistance. The thermal fuse p/n (###) ###-#### measures 0.4 ohms and it's also new.

Okay, do you have your diagnostics/tech sheet? If so look on it and see if it tells you what the thermistor reading should be depending on the surrounding temperature. I am going to look for my diagnostic sheet also.

Customer: replied 4 years ago.

Assuming p/n (###) ###-####is the exhaust thermistor, and given it's placement it must be, the spec’s resistance is 10k ohms. There's no temperature spec for this component that I can see.

Okay, do you happen to have a hair dryer? If so you need to blow it on the thermistor for 2 minutes and see if the reading goes up. Right now it looks like it is bad as the reading is too low. At room temperature it should be reading about 20Kohms.

Customer: replied 4 years ago.

Better yet, I have a heat gun. I'll keep it low and check frequently so I don't melt anything.

Okay, the resistance should go down and at 80 degrees room temperature it need to be about 10K. Let me know what you find.
Customer: replied 4 years ago.

Okay, I found a couple of things; resistance dropped way down if I overheated it but comes back to 20k if I set it where it can cool down. The ambient temperature in the laundry room is on the warm side so that's why I think the initial reading of 12.6k was accurate. FWIW, I also tested the old one, which was also sitting in the laundry room, and it reads between 11 and 12k.