Furnace Troubles

It all started on Tuesday morning when my wife heard a strange and loud noise from our furnace. She took a picture of the exhaust vent and texted me, asking if the steam coming from the vent was normal:


The steam was normal, I said, but the noise concerned me. That night, when I got home from work, it was still happening. It was a clanking, rattling noise that was so loud that we could easily hear it when sitting upstairs in our living room watching TV. I went down to the basement and took this video up close:

I read a few articles online and one troubleshooter suggested changing the filter. Our wasn't that old – I'd changed it a month or two ago – but I tried just in case. I also powered down the furnace using the emergency electric cut-off switch, waited a few minutes, and then started it back up. The noise was gone. Problem solved. Or so we thought…

On Saturday morning at 1:00 a.m., my wife woke up to feed our month-old baby and found that cold air was blowing out of the vents and that the temperature in the house had fallen to 65°. By 6:00 a.m. the temp had fallen to 63° and she woke me up to tell me what was going on.

Downstairs, I found that the fan was still blowing, but that the blue flames inside the furance itself were missing:

furnace vent

I called my dad and asked for advice. He suggested looking for an indicator light, seeing if there was a pattern and, if there was, looking in the manual to see what it meant. I found the light on the bottom panel of the furnace:

furnace indicator light

Turns out, the red furnace indicator light uses Morse code to spell out a problem number, which you can then look up in your furnace's owner manual. Our light was blinking 6 times:

I found the owner's manual for our furnace, and it said that 6 Flashes meant that the rollout limit circuit was open.

furnace owner manual troubleshooting guide

I found a few articles online suggesting tips for how to remedy that. One suggestion was that I check the incoming air vents for any obstructions. That was my next step, but it didn't lead to anything; the pipe was clean.

furnace intake vent

inside of furnace intake vent

At that point, I realized that I needed to call an HVAC expert, but it was the Saturday after Christmas, so everyone was running on emergency rates and had little-to-no availability. After checking several reviews and calling around a bit, I finally got ahold of a guy who not only guaranteed that he could make it out that day, but also offered a bit of troubleshooting over the phone. When I told him that the the rollout limit circuit was open, he suggested that I reset it.

After a bit of research, I discovered that the rollout limit circuit is a safety mechanism that helps to shut off the furnace when things aren't right. Although this can be very helpful, it can also be the source of a false positive – the rollout limit circuit itself can go bad. So, a good troubleshooting step was to reset it and see what happened.

There were two rollout limit circuits that I could find in our furnace:

furnace rollout limit circuits

I pressed the button on both to reset them and found that the one on the left was, in fact, open. It clicked when I pressed it.

furnace rollout limit circuits

"Sweet! Problem solved," I thought… I turned the furnace back on to see if that had done the trick. Nothing happened.

After almost a minute with nothing happening, I decided that I should probably cut the power and wait for the HVAC guy to get there since I didn't really know what I was doing.

When he arrived, the furnace started right up for him with no problem. D'oh! I was thinking that I simply hadn't waited long enough after reseting the rollout limit circuit. But, before I could spend too much time feeling like an idiot, the furnace acted up – badly – and I learned that I had made the right call by being cautious.

The furnace's main blue flames were pouring back out towards us; a situation that seemed very dangerous. He switched the furnace off right away then explained to me that the primary heat exchanger was busted.

He wanted to double check a couple things so we waited a couple minutes and then started it up again. This time, it was working perfectly. Weird. He turned it off and on again, and the same thing happened; it was working just fine.

But, on the third try, after removing the bottom panel again, we saw the problem again clearly:

Because it was a holiday weekend, the soonest we could even hope to get parts was Monday. So, we were facing at least two days with no heat, maybe more. What a fun holiday surprise…

Just to make sure we understood the severity of the situation, the HVAC guy made me sign this note saying that I was aware that using the furnace before it was fixed would cause "loss of life and property." Gulp.

a warning

The new heat exchanger wasn't available locally, but they were able to overnight it and it arrived Tuesday afternoon. The HVAC company sent out a guy Wednesday morning to install it. A couple hours and $675 later (the warranty covered the part itself, but not the labor), our house finally had heat again!

This post was published on December 27th, 2014 by Robert James Reese.