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thealexdexter 12-05-2008 11:59 AM

Payne 480BAV:Error 31

I recently had a repairman tell me my control board was bad, the hot surface igniter was reading high, and the inducer motor bearings were going out...and I need a new furnace due to cost to fix. I decided to repair it myself and now I'm a bit stuck.

I replaced the the control board and igniter with OEM replacements. The inducer seems fine to me so I left it alone for now. Upon restart I disconnected thermostat wires and shorted the test to com terminals to initiate a test routine. The igniter worked, the inducer spun, the blower turned on for heat and cool other words all was fine in the test.

I hooked up the tstat and let it go through a normal startup. It did a 90 second prepurge with the blower (normal) then the inducer started up. But the igniter never fired and I got error 31. So I shorted RW tstat wires to force a call for heat...same problem, error 31. I then cleaned the flame sensor with steel wool and checked the voltage going to the inducer, it was 124VAC.

I checked the hose on the pressure switch for obstructions or cracks...seemed fine. The voltage across the pressure switch terminals was 3vac before the inducer kicks on, then 0vac after the inducer, so I think the switch is fine. Although I don't know about those voltage readings. Should I measure each terminal referenced to earth ground seperatly or measure across the terminals? I also know it is a 24vac systems so I was expecting 24vac not 3, but maybe its the way I'm measuring.

Any thoughts on how to find the cause of the error code?
How do I know for sure the inducer motor is working, I see it spinning and I know its getting 120vac...but that's it.

My venting is a 4" metal pipe that goes straight up to the roof.

Thanks for any help!

SKIP4661 12-05-2008 06:02 PM

I believe it is a pressure switch fault. There should be a label on one of the panels that tells you the fault codes.
You can test the switch by jumping acrossed the common and normally closed terminals after the inducer starts. If this works you will need to check the venting for obstructions (dead birds). If no obstructions check the spud on the inducer where the pressure switch tubing connects, sometimes the spud will plug up. Do not leave the switch jumped out as this could cause serious problems.
Good Luck.

thealexdexter 12-05-2008 06:09 PM


I forgot to mention I did jump over the pressure switch terminals. I did this before I turned the furnace on though. Does it matter if I do it after the inducer starts vs. before? It did not seem to make a difference doing it before, same error code and ignitor wouldn't go.

I did not check the spud..I'll do that and the birds when I get home.

i checked the 31 fault code: it says it is the inducer, pressure switch, venting, gas pressure, etc. Basically everthing under the sun.

I've been reading about limit switches. Where are these located on the Payne 480BAV? The only switches I seen are the pressure and the cabinet door switch...are there others?

yuri 12-05-2008 06:15 PM

code 31 is a pressure switch open code. You can take the 2 wires off of it and tape them. Then put an ohmeter across the switch and fire it up. If it shows no resistance then it is closing properly and is okay. If not you may need a new switch and they do fail. I used to do lots of Carriers and changed them. The only other way to know for sure it to hook up a manometer to the press switch hose and check the draft. It usually needs a minimum of -.45" wc to close. Check the chimney for obstructions. You cannot jump it B4 the unit starts as the board needs to see an open switch or it will lockout.

SKIP4661 12-05-2008 06:20 PM

The Circuit board needs to see an open pressure switch circuit before the inducer starts or it will fault. Should also check for moisture in the pressure switch and tubing.

HvacWiz 12-05-2008 07:35 PM

Also check for plugged condensate trap, If it isnt draining condensate will get into the collector box and not allow the switch to close on call for heat.

thealexdexter 12-05-2008 11:14 PM

OK heres where I'm at:

1. The top 5' of the vent at the roof is not plugged nor is the bottom 5' right off the top of the furnace. When the vent was off the furnace I stuck mu vaccum cleaner hose in there to clean out the small pebble/debris. Doing this made the inducer wheel turn, I think this means the inducer blades on the inside are also turning thus more indication the inducer is fine.

2. open reading in ohms across the pressure switch when nothing is on. Extremely high (mega-ohm's) when the blower is on and the inducer is off. 0.4 ohm after the inducer starts. (0.4 is about the resistance of the wires I'm using so it's basically 0 ohm.

3. Checked tube and nipples at switch and vent wall. No cracks or obstructions. I was able to blow through the nipple into the furnace easily. I also sucked on the nipple on the end of the switch. It took about as much force as taking a hard drag off a cigarette to make the diaphragm move. With nothing on I measured the resistance across the switch by blowing/sucking on it and it basically went from open to 0 ohm. Seems like the switch is fine? It made some crinkly paper sounds when the diaphragm moved.

4. I jumped across the switch after the inducer started. This did nothing, just like when I jumped it before I turned the furnace on. Same error 31.

5. no moisture in tubing, how would I know/check if there was moisture in the pressure switch. Gently shaking it did not indicate a water.

6. I do not have an AC unit so I don't think there is a condensate trap. If there is one, where is it?

7. I operated the furnace with the tube to the pressure switch removed. I could not feel any suction of blowing air coming out of the hose either before or after the inducer turned is really so small I couldn't feel anything?

8. Thre is a small pcb with two spade termiansl on it with red wires. I think this is some sort of thermal fuse? I put the ohm meter across the "thing" that I think is the termal fuse when nothing was on. It read about .8 it was letting the electricity through at room temps. Is that what this thing is?

If I jump across the pressure switch, this basically eliminates it from the system in case it's broken right? If so, wouldn't that indicate some other function "down stream" of the switch is broken? What happens after the switch closes...I think that's what I need to investigate next.....

There is a draft safety switch connected in series with the pressure switch. Should I jump across that so I take it out of the system at the same time as the pressure switch...doing so might indicate the DSS is bad...

SKIP4661 12-05-2008 11:38 PM

Where is this round thing located. It could be a spill switch or vent safety. Pics would be great.

thealexdexter 12-06-2008 12:04 AM

1 Attachment(s)
pic is attached of round thing...

also, should I check fresh air inlet pipe for obstructions too or just exhaust vents

thealexdexter 12-06-2008 12:06 AM

1 Attachment(s)
close up of round thing

thealexdexter 12-06-2008 12:08 AM

1 Attachment(s)
This is close up of what I think is thermal fuse

NYCtinman 12-06-2008 01:05 AM

If you have done everything --- jump out the switch(s) check the flue (chimney) clean the drain lines & make sure you have gas (ck the stove) I would replace the control board

beenthere 12-06-2008 04:52 AM

The furnace must be running for a few seconds before you jump the pressure switch.
Push the DSS reset switch in, and see if it makes a difference.
If so, then you need to find why it tripped.

thealexdexter 12-06-2008 04:52 AM

The control board was the first thing I replaced.

Maybe something is hooked up wrong???? Guess I could check it again.

There is a mechanical damper on the inlet side. It seems very stiff to open to me by pushing on it. Is this motor controlled or just air pressure normally? The rest of the fresh air inlet is debris free.

yuri 12-06-2008 09:01 AM

If you changed the board and they gave you the newer version which is a retrofit and has extra wiring harnesses you may have a poor connection on one of the molex/connector plugs. Carefully remove them and look at them with a magnifying glass to see if any of the pins are pushed back. Post a pic of that mechanical damper here. Sounds like a Hoyme damper which is interlocked with the furnace. If it is on the combustion air pipe it is a mechanical damper which should open with the furnace. Don't push it or you may strip the gears. There is no condensate trap/you don't have a high efficiency furnace.

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