Strange Problem with My Two Year Old Furnace

[Qs Laptop]

I had a weird issue with my 2 year old Trane furnace last night including a mystery inside the cabinet.

TLDR: My furnace wasn't running last night, my Ecobee thermostat readout was black. The fix was to pull the 5 amp fuse on the furnace control board and reinsert it back in place.

Last night watching TV I noticed I was cold. I checked the Ecobee thermostat app on my phone and it said there was no wifi connection. I went upstairs and checked the thermostat and the readout screen was black. Googling showed there should be 24v to 29v AC between pins C and RC. I grabbed my voltmeter and checked and saw only 10v.

Next step is to check the error codes on the furnace control board. The readout on the control board showed 1 DL. "One Dee Ell." Oh, that means "Idle", which is the normal state of the furnace when it is not running. In other words, no error codes at all.

Next step is to check the 5 amp fuse on the furnace control board. If that was bad it would explain why I'm not getting 24v AC at the thermostat. I flipped the circuit breaker off for the furnace. I removed the front panel of the furnace (had to YouTube how to do this!) and located the 5 amp fuse. Funny, but there was also an identical 5 amp fuse lying on the floor of the furnace housing. I thought that was both strange and fortuitous as it was almost 9 pm and I doubt I could find a store open on a Sunday night to buy a new fuse. Looks like the installers left me a spare. Awesome.

But wait a minute...why would they put a spare fuse inside the furnace box? Is this fuse blowing a known issue? Anyway, I pull the fuse on the circuit board and test it with my ohmmeter. It's perfectly fine. I test the "spare" fuse that was inside the furnace box. It's open, it's no good! WTH?! I visually inspect it, Yep, it's bad. Why is there a bad fuse inside my (mostly) new furnace box? Obviously, left there by the install techs.

I reinsert the original fuse into the circuit board, flip the circuit breaker to On, and the furnace starts to go through the start-up cycle. But now I see an error code, E3.1, which means a problem related with the low pressure switch on the AC unit outside the house. I'm in Minneapolis and the AC has not been turned on for at least 6 months. Furnace comes on, heat is working again. I checked for the error code after the furnace cycled and it had cleared out. I'm back to 1 DL.

Apparently pulling the fuse and reinstalling it is the equivalent of "did you turn it off and turn it back on again?" method of fixing something.

Comments? Suggestions?

 

[omni550]

Perhaps you dislodged a slight corrosive area? Just guessing. Sort of like cleaning the contacts.

omni

 

[pb4uski]

...Suggestions?

Call the repair guy.

 

[Jerry1]

Suggestions?

Get another fuse to have on hand.

 

[street]

Furnaces have a pressure switch they can be problem like you are describing. Also, the mother board may have an issue with a soldering connection that when it runs for a while it gets hot/warm and shuts things down.
These two examples of possible issues have been the case for a few people that I know and with the same symptoms you have mentioned.
Reach both possible causes that I mentioned, pressure switch & mother board causes of failure. Not sure either are your issue but like I said both have been an issue for others that I know.

Furnaces have a lot of safety issue shut down defenses.

 

[isisdave]

Possibly it was the cycling of the power via your circuit breaker that resolved the problem. In other words, you rebooted it.

 

[Qs Laptop]

Perhaps you dislodged a slight corrosive area? Just guessing. Sort of like cleaning the contacts.

omni

Possibly, but if so, it would have to be the fuse holder area.

Call the repair guy.

I can do that, but I believe the first thing they will say is "what error code is it throwing off?" And I'll say none. But, yeah, they might have seen this problem before and give me some direction.

Get another fuse to have on hand.

I definitely will do that.

Possibly it was the cycling of the power via your circuit breaker that resolved the problem. In other words, you rebooted it.

I don't think so. Because I turned the circuit breaker off and back on again BEFORE I pulled the fuse out. This was mentioned as the first troubleshooting step, which I did. It was only after I pulled out the fuse and reinserted it, that it started working again.

 

[Qs Laptop]

Furnaces have a pressure switch they can be problem like you are describing.

Yes, But the error code is related to the outdoor AC unit, not the furnace itself.

Also, the mother board may have an issue with a soldering connection that when it runs for a while it gets hot/warm and shuts things down.
These two examples of possible issues have been the case for a few people that I know and with the same symptoms you have mentioned.

I sure hope it's not the motherboard as those cold solder joints are hard to find. I guess that's what 10 year warranties are for.

Furnaces have a lot of safety issue shut down defenses.

Yes, I ran into a bunch of them with my previous Carrier furnace.

 

[djsander]

I would just play dumb when they ask about error codes. It’s 2 years old and still under warranty. Just call them to look at it. I only do minimal trouble shooting anymore.

 

[bloom2708]

The first thing I check is if my two vents are free/clear of frost/ice/snow.

If done correctly, the two vents should not interfere with each other and frost up.

If the vents are clear, then you can look up more information on the fault code.

After I checked a few things, I'd call my furnace company and get them out. Parts do go bad, even on newer furnaces. The long/cold winters are tough on things up here in the north country.

 

[Winemaker]

When were the batteries in the thermostat last changed?

 

[Qs Laptop]

I would just play dumb when they ask about error codes. It’s 2 years old and still under warranty. Just call them to look at it. I only do minimal trouble shooting anymore.

I could do that but then I'd have to explain what happened and what I did to the furnace last night. I guess that's no big deal. I be surprised if they'd sent someone out to look at a working furnace with no error codes.

The first thing I check is if my two vents are free/clear of frost/ice/snow.

If done correctly, the two vents should not interfere with each other and frost up.

If the vents are clear, then you can look up more information on the fault code.

After I checked a few things, I'd call my furnace company and get them out. Parts do go bad, even on newer furnaces. The long/cold winters are tough on things up here in the north country.

The vents are free of frost/ice/snow. We had a heat wave here in Minneapolis last week. Highs were in the upper 40's. It did dip down into the 20's over the weekend but we're at 47F right now.

The fault code E3.1 description from the owner's manual:

Since the furnace has been running flawlessly for 2 years I'm fairly certain the wiring is correct. Not sure what tube routing is, but I'm going to guess that is correct as well. The next step is to check to see if the pressure switch is shorted, but I'm going to assume it's not since the furnace is working.

I remember with my old Carrier unit there was a possibility the pressure switch would close if there were gusts of wind. I never had that happen and anyway, it wasn't windy here last night.

When were the batteries in the thermostat last changed?

No batteries in the Ecobee Smart Thermostat. First thing I looked for and was a bit taken aback there weren't any batteries.

 

[ncbill]

Posts like the OP's are why I'll hold onto my 80% furnace until you pry it from my cold, dead hands...

 

[Time2]

Possibly it was the cycling of the power via your circuit breaker that resolved the problem. In other words, you rebooted it.

I second this motion!

 

[Stormy Kromer]

Make sure your CO2 detectors are in good working order and then have the people who you bought the furnace come out and fix the problem for you.

Since the furnace is only 2 years old the dealer you bought it from is likely in business and can help you if it is a warranty issue.

There are a lot of things I'll attempt to fix on my own except anything that deals with gas or electricity.

Let the pros handle this one and sleep well. Be safe, and warm.

 

[gauss]

Posts like the OP's are why I'll hold onto my 80% furnace until you pry it from my cold, dead hands...

Exactly.

My 40 year old furnace has wiring diagrams on the inner panel that I have used in the past to "reverse-engineer" the operation. I havereplaced many "generic" components over the years (pressure switch, igniter, main blower motor, capacitors internal to secondary blower (ie draft inducer) ..) And that does not include all the work done on the central air conditioner.

Surprisingly the electronics have held up, but it is a generic White-Rogers control unit in a separate box.

-gauss

 

[GrayHare]

But now I see an error code, E3.1, which means a problem related with the low pressure switch on the AC unit outside the house.

Have you used cooling yet to know if it is operational? Is this unit a heat pump? IIRC some units temporarily go into cooling mode during winter in order to perform a defrost.