# Troubleshooting Carrier Furnace code 31



## how

31 = pressure switch. Checking for a debris build up inside the ID assy port that the hose from the PS is attached to, is a more common DIY fix. Make sure nothing is blocking your vent exhaust or intake.
Beyond that it can be 30 or more other possibilities.
A manometer check against the rating on the PS tells if the problem is with a faulty Pressure switch or the furnace.


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## oldducts

Nothing blocking the vent exhaust or intake. Not quite sure where you are suggesting I check for debris - happy to check if I can figure it out though. (I have to admit, I am not sure where the PS is.) 

I did check the condensate trap, and that seems to be blocked. (I disconnected the output hose from the trap, and it was dry, but I disconnected the input (largest of the three hoses attached to it) and quite a bit of water drained out.) Assuming that indicates that it is blocked, what is the best way to clean out the condensate trap? Is there a trick to removing it? 

Thanks for any further assistance. Hoping for heat tonight....


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## oldducts

Okay, I was able to remove the condensate trap. It was definitely clogged. ran some water through and shook it a bit until a bunch of "debris" came out then water ran through it cleanly. Have put it back together, and it is running so I will see what happens. 

Will be back if this didn't work. In the meantime, let me know if there is anything else I should check. 

Thanks.

Chris


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## jagans

Your trap and the lines to it are probably full of crap. 

Take off the hose clamps remove the hoses to the trap and clean out the hoses by submerging them and trap in sudsy bleach and warm water and clean everything well. Be very careful removing the hoses that you don't break off the plastic nipples. Suck out the secondary HE drain with your shop vac. When you put the trap back, prime it with water and a little bleach.

Make sure your vacuum hoses are not cracked or stopped up also blow them clear with compressed air. Make sure the hose barbs on pressure switch are not clogged. Also clean electrical connections.


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## oldducts

Possibly a stupid question except that I am not sure of the answer. Water from the inducer hose drains through the condensate trap just fine, but water from the collector box hose does not drain. Should it? 

Am soaking parts now and will be checking vacuum hoses.

Thanks for the help.


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## oldducts

Update:

1) Last night after work, I got home to code 31. I removed the condensate trap, and ran water through it until I got water running freely from the inducer input to the output. Reinstalled, set up the drain to drain to a bucket so I could verify it was draining, turned it on, and it ran fine for several hours.

2) At some point during the night, it threw the code 31 again. The bucket did confirm that condensate was draining. 

3) Removed the trap again this morning. The hose from the inducer to the trap had water backed up. Removed the trap and soaked it. Did not appear to remove debris, but it does drain (from the inducer input - not from the collector box input if that matters). All vacuum hoses to the PS are clear removed and reinstalled the electrical connections a few times. Was able to elicit a click on the PS with gentle blowing into vacuum tube. As far as I can tell the barbs on the PS are clear.

4) put it back together, and it starts fine. Inducer motor works fine, burners fire, blower comes on. I now expect that it will work for some period of time and then stop.

Any further suggestions?

I am learning a lot - thanks.


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## jagans

Most definately. The black plastic collector box covers the end of the secondary heat exchanger. You may have to remove the inducer motor or better yet the collector box to really get the insides clean. You may be looking at a secondary heat exchanger that has been recalled by Carrier. If it is coated with polyester paint, the ends of the secondary heat exchanger tubes start to peel and rust, and the stuff clogs up your condensate drainage.

The problem comes when you try to remove the collector box. The sealant they used hardens and it is very easy to break the box in the removal process, but it can be done. I sprayed mine with WD-40 several times and it seemed to break down the sealant to some degree, I then removed the box by applying continuous gentle pressure with two wonder bars. 

First try to remove the inducer fan, this will give you some limited access to the end of the secondary HE through a half moon shaped hole. AGain spray and apply gentle pressure till it starts to give. Spread the load with a metal plate behind the fulcrum.

You can get a plastic toilet cleaning brush in there by reshaping it, and you can vacuum out the crap with a shop vac with some creative tubing. 

I ended up taking off my collector box which I cracked, I wire wheeled the ends of the tubes, and resealed around the ends of the tubes with GE fast cure clear silicone. My HE leaked, and this solved it. 

I patched my collector box with fiberglass drywall tape bedded in the aforementioned silicone, and patched the outside with pressure sensitive EPDM Tape. All Worked great. HE no longer leaks, condensate drains well.

A clogged condensate line fried my board, which has been replaced along with my HSI and a pressure switch. Furnace now runs great.

I like Carrier a lot, but that polyester coating was dumb. SS would have been better, and less expensive in the long run.


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## oldducts

Thanks! I think I understand the mechanics of what is happening. The condensate trap is still clogged an is not letting the collector box drain. So I have come along twice and drained the collector box. That works fine until too much condensate builds up again. Is there any trick for more thoroughly cleaning the condensate trap or might it need to be replaced assuming I can't get water to flow from collector box through the trap.

I will take a look at the collector box and secondary heat exchanger. My understanding from the serial number is that this unit was made in 1996 so I believe it would be eligible for replacement. Will see about removing collector box. Don't want to break it. Will remove inducer fan and see what I see.

Thanks for any further info on the collector box and condensate drain.


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## beenthere

Hot water and Ivory dish soap. Shake vigorously. Let set, repeat. Dump out dirty soapy water, flush the trap with clean water in all directions. Put it back in furnace and run furnace.

Are you on natural gas, or LP.


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## jagans

Well there was a class action suit on the secondary HE. Mine was made in 1993, and I qualified for $124.00 as it was pro-rated. I said Wowee what a deal! and proceeded to fix mine myself. The cost to replace the HE at this stage of the game just is not worth it.

As with most class action suits, the attorneys take all the meat, and leave the plaintiffs with the bleached bones. The end result is Carrier raises the price of their parts to make up for the loss.

What do you call 2,000,000 dead Lawyers? A good start.


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## jagans

Yeah you need to really clean the trap. Just remove the two hoses, take out one screw in the bracket and remove it. I used dish soap, TSP, and Bleach in warm water, but I guess Ivory will work too. I needed more horsepower.


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## oldducts

Thanks everyone. Soak, shake, rinse, repeat finally worked. 

I have been good for over 24 hours now. Of course I haven't fixed the underlying problem. I elected to quit while I am ahead and not try to get at the collector box or secondary HE. I will see how long it is until it clogs again. 

beenthere - the system is natural gas. 

jagans - interesting information on the prorating of payment on the HE.

very cool to have a better understanding of how the furnace works.

Best,

Chris


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## pbb

google brought me here. wanted to share my experience. 19 y/o carrier. upon removing the air filter noticed some water stains on it but nothing recent. pulled the 2 hoses off the pressure switch and blew into them. top one clear. bottom one heard bubbles. discovered the condensation trap was half plugged up. there were 3 hoses going to mine- and relief, inducer and collector box drains. the collector drain was full of water. removed the trap and spent an hour letting it soak and force water/ air through the side that was plugged. lots of black organic material came out.
been working fine the past 24 hours.
and regarding the heat exchanger "warranty." when i asked my local shop about it they confirmed not just a 20 year but a 25 year warranty. but when pressed for details they didn't mention labor coverage. so i believe the "enhanced warranty" that includes labor is just for 20 years, and will likely take advantage of it before mine expires to prevent confusion.


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