The pressure switch is a small round part,it has two wires running to it with a small rubber tube attached

Hi,
No tubes going into the inducer fan at all, at least not from the front or sides. There is a place at the upper right corner where you could put a tube in. In the manual it says this is where you pour tap water to prime the system drain before you start the furnace, but there is no tube in there now. I see a little drop of water in the hole, which is open. No plug in it, as I think there is supposed to be.

I've attached the photo. The disconnected tube is hanging out the front of the furnace, and in the lower left hand corner of the main compartment you can see where I plugged a little wad of white paper towel into the hole in the front of the furnace. That tube comes out the back of the pressure switches.

The two silver round parts with a tube between them is the pressure switches. Reconnect the drain.

Here is a pix of the whole front of my furnace.

Sorry, a little fast on the trigger. I reattached the hose.

The small rubber tube hanging in the front,where was it connected?

You see that kind of u-shaped tube that goes into the front of the pressure switches? If you look at the back of the pressure switches, there is an identical little u-shaped hose, but there is a t-connection in the middle of it and that tube comes out the back, and the other end goes into the front of the furnace where the paper towel is.
I didn't see any other tubes from the pressure switches that went into the front face of the furnace. The one that comes out the side and goes upward is plugged into what looks like the part that brings gas into the furnace.

Ok. Put all of that stuff back together. Next, check the intake and exaust pipes from the furnace all the way to the basement wall, make sure there are no bellies in the pipe that might be holding water.

Will do. Be right back

Hmm. Both pipes seem completely straight to me. It is a pretty long expanse, about 20 feet maybe, from the furnace to the outer wall. The pipes are supported by hangers, which sounds goofy, but it all looks very solid to me.
I was outside and could see nothing in the tubes. The tubes are 3" diameter, pretty big.

Ok, should be fine then. How long has it had this problem? And does it always give you the same code?

Now that the tube is back in place, is it OK if I turn the furnace back on? It is getting kind of cold in here.

Well, let's see how it does tonight since you drained all of the water out of it,I will check back with you after work tomorrow to see how it did. It's late here and I need to get to bed.

Yep, turn it back on

No, mostly it gives me 31, sometimes 32. Once or twice it gave me 42, which means blower calibration fault, but mostly it is 31 and 32.

This problem started sometime in the middle of the night last night. When I woke up it was 59 in the house. I have the thermostat set at 65 late at night. That night we also had a snowstorm with a lot of wind.

Thank you so very much for your help. I appreciate it. Sweet dreams.

And it hasn't ran right since?

Correct. Go to sleep! I don't want you to be without sleep tonight. We are in the same time zone, it is late for you to be up if you work mornings.

Good morning,
I'm heading into work myself this morning, but thought I'd mention how the night went. It is working a little better. The furnace will cycle into the low heat mode and run for quite a while, then it steps up into the high heat mode, where the blower blows harder. It used to be that would kill the furnace, as soon as it would switch into high heat mode it would get the 31 code and shut down. Then maybe make a few more starts and quit.
Last night it ran in low mode fine, went into high mode, then got the 31 code, shut down. When it started up again, it ran in low mode then went successfully into high mode for at least 20 minutes. Stronger airflow, hotter air coming out of the registers.
But now it is back to the same problem, though it seems to run a little longer before it gets the 31 code and shuts down.
The house is staying a little warmer, 63, as opposed to 59 last night.

I have to go to work in a bit, will be home in the pm.
Thanks for giving this your thought.

Just checking in,I'll check back shortly to see if you are around.

Hi my friend,
I was wondering if all that water that drained out of the collector box last night when I took off the pressure switch drain tube indicated that maybe the drain trap or some part of the drain tubes were clogged.
Im not sure how to clear out the drain trap.
Just to test this idea, when I got home I took off the same tube again, the one from the pressure switch to the collector box. Again, water flowed out of the tube and the collector box, 2 cups at least.
Then I took the inducer housing drain tube off its drain plug. Nothing came out there.
I am thinking there should not be so much standing water in the collector box, something must be stopping it from draining. Does this sound right to you?
Do I need to go to the drain trap now?

The trap should be flushed at the beginning of each heating season as part of the required maintenance for the unit. If you experienced condensate migrating through the pressure switch tubing, the switch canister may have water inside and will eventually fail. Take the pressure switch off and give it a shake to see if water comes out. If so, I highly recommend replacing it. And, you're correct about water accumulating in the collector box-this is a sign that it is not draining properly.

Sounds like too much water your trap is the white thing at the bottom of you pic. It hangs down into the blower compartment. Take it off and clean it out with water. And the hose coming off that going to the drain clean that out (flush water or blow it out)

Hi,

I think I got it, thanks so much for the invaluable help. Until I found this site, I was really bummed. I just did not have it in my budget for a $300 service call 2 weeks before Christmas. Would have been pretty thin pickins under the tree. Your helpful advice gave me the confidence to do it myself. Now I feel pretty handy.

Couldn't figure out how to get that drain trap out, so I took off the biggest tube, the collector box drain tube I think, and blew a bunch of water through the drain trap. I got a bunch of gunk out and when it seemed clear, I put the tube back on.

Turned on the furnace and it so far seems to be working fine.
The first 10 minutes or so it ran, a gurgling sound came out of the drain tube, but it quit after a few minutes.

KC13, I don't feel confident enough to take the pressure switches off, but since the furnace seems to be running OK, do you think it is OK if I wait until spring to make a preventive service call? Christmas and all that...

Greg HVAC guy, do you work the northern suburbs, like Highland Park? That's where I am. If so, give me your co name and I'll call you then.

Than

The question you must ask yourself is, do I feel lucky? Well do you? C'mon man, you've come this far, check those switches! If you look closely at the pressure switch hoses, they should have labels to identify where they go. The switch assembly mounts to the front of the inducer with two 1/4" zinc-plated screws (yellowish color). Take 'em out, pull the labeled hose off the tee in back, and shake the switch assembly. If you hear water inside, drain out as much as possible and replace the switch assembly as soon as possible. If not, then answer yourself-yes, I do feel lucky!

Well, it is supposed to warm up this weekend, so I guess I could shut the furnace down for an hour or two.
When you take those screws off, the 2 switches and the bracket all come off in one piece? I don't have to take the wires off the front?
If I hear water, I'd drain it out the holes where the rubber tubes connect, I guess?

Yes, the switches are an assembly. If one is bad you replace both. No need to remove wires yet, just the screws and the hose on the back so you have enough movement to detect water if present. Confidence! Or draw a pic, works just as good...