Furnace Problem. Any ideas?

Factual Questions
1

My furnace is 3 years old. It’s a Goodman brand. Last night I discovered cold air so I investigated and find that my furnace’s flame keeps kicking itself off then a few seconds later, tries again.

So it kicks on as normal, I see the pilot light, then the orange glow of the flame firing up then the fan kicks on. It then appears the pilot is kicked off after a few seconds and within maybe 10 seconds, the pilot lights up and this process keeps repeating itself.

So my house is getting quite chilly. I shut it off for now to determine if it’s something simple I can do myself or if I need to call someone.
My co worker suggested it might be a thermal coupler but looking through the manual, I don’t see any parts that say thermal coupler, closest I see is inshot burner.

The troubleshooting guide is pathetic but there is one part that mentions “Flame Sensor” saying it can sometimes get an invisible coating, insulating it causing a drop in signal. If it drops too low, it will not sense the flame and drop out…is this what mine is doing?

Anyone else have any ideas? I’m mechanically inclined but I just don’t know a darn thing about furnaces or exactly how everything works.

2

It’s called a thermocouple, and here are photosof what various models look like.

Yeah, it could be a thermocouple, but it could be other things, too. And if you don’t know anything about furnaces, you’ll end up calling a repairman anyway. It’s January and it’s cold, so I’d just bite the bullet and call now.

3

There’s a handful of things that need to happen for the furnace to fire normally (and stay on). It could be the flame sensor (which you can remove and sand to clean), but it doesn’t sound like that’s the case. Typically, if that’s the problem, the unit will turn off before the main blower turns on. I assume you’re talking about the main blower and not the small inducer motor near the top that starts up at the very beginning.

If you want to troubleshoot further, take the bottom panel off and you’ll see a box. The box may or may not have a little window. If it does you should see an LED. Not the color of the LED and count the blinks. Then remove the cover and there should be a legend explaining what’s wrong. Keep in mind that, if you don’t cut the power to the furnace, there’s live wires in that box so don’t touch anything on the panel.

If it hasn’t run in a while, you may have to hold the safety switch down with your finger to get it to start (and then stop on it’s own) so the the trouble code shows up again if it’s not already displaying.

4

Sounds like either the flame sensor or the high limit switch; probably the former.

5

Thanks, I fixed it. House is getting warmer already.

6

What did you do to fix it? In the interest of other people who stumble upon this thread or people like me who can help to tell you if what you did fixed it for good or just fixed it temporarily. For example, if you sanded the flame sensor a bit, I’d highly recommend you go out and buy a new one as soon as you have some time, OTOH, if you replaced your pressure switch with a new one, you’re good to go.

7

HeXen and all;

A 3 year old Goodman or any furnace will not have a standing pilot or a thermocouple. There are 2 types of modern gas fired furnaces.
1: Conventional 90% efficient, has a metal vent pipe and a combustion blower motor. Pretty reliable and easy to diagnose, or
2: High Efficiency 98% condensing with a plastic vent and maybe a plastic inlet air pipe. Condensing refers to the combustion gas and the water that condenses out of it.
Both types have a direct ignition system. Most common is a hot surface ignitor and separate flame sensor.
Normal sequence of operation is-
1: Thermostat calls for heat- 24 volt signal to electronic ignition/fan control board.
2: Board energizes the combustion blower motor, the small motor you can see.
3: Air flow through the combustion chamber closes the pressure switch circuit.
4: With the pressure switch closed the controller energizes the 120 volt hot surface ignitor, that’s the red glow you see. The ignitor is energized for at least 20 or 30 seconds before the controller energizes the 24 volt gas valve.
5: The flame sensor must detect a flame within 2-5 seconds. If it does, the valve stays energized and the indoor circulating fan will energize after a short delay.
If the flame sensor does not report a flame, the controller will shut off the valve, leave the combustion fan on to expel unburned gas, wait 30 - 120 seconds and try again. Most controls will try 3 times and go into a failure mode.
6: If the control cannot establish ignition after the 3 tries it will energize the circulating fan continuously to get your attention.

Most boards have a blinking LED to signal the fault code. There should be a list of blink codes on the furnace. Some are fast/slow, some are one speed. Like 3 fast, 2 slow, wait, 3 fast, 2 slow… repeat, is code 32. Or 8 fast, wait, 8 fast…repeat, is code 8. Very few show more than one code at a time. If you have multiple problems, the second code will not show up until you resolve the problem causing the first fault.

Flame sensors are pretty robust, just a length of wire sitting in the flame. It is just a conductor. It conducts a 2 - 30 micro amp current to ground.
The ignitor is very fragile. It’s silicon carbide and will break easily.
Check the ground connection to the flame sensor. Check the nipple that the pressure switch hose connects to on the combustion blower housing. The inside can get covered over by a film of combustion products. Stick a drill bit or Allen wrench into the hole (fan off).

If you have a Goodman with 2 pressure switches you have a real treat. Don’t mess with it, call a service tech.

Goodman started out in Texas I think, in the 80’s. It was crap. Slowly got a bit better. Started offering pretty good warranties. Got better. In the 21st Century, Goodman, Coleman, York and a couple others I can’t think of are all one big happy family. I don’t know who bought who, but recently the whole thing was bought out by Daikin.

“Don’t pick your furnace by the name on the box. Go with the name on the truck.” I didn’t say it first but it’s the best advice anyone can get when selecting an HVAC system.
Most brand name equipment is just about the same. Proper system design and proper installation are the most important criteria.

Hope this makes some sense.
Matt

8

Don’t that just burn your ass when people do this?

“Everything’s fine now, bye!”

9

What bugs me is when I’m trying to fix something (say, a problem with my computer) and I find someone else in the internet that asked the same question, say, "my computer won’t boot, it just stops mup.sys and after some troubleshooting questions from other forum members, they’ll come back and say ‘fixed it, thanks’ and that’s it. C’mon, what’ja do?

Obligatory XKCD.

10

This thread is so…

Unsatisfactory.

HeXan may be kicking back enjoying his heat, but if he doesn’t respond within 48 hrs (and he hasn’t been killed by a gas furnace explosion or asphyxiation by natural gas), should his posting priviledges be discussed? :smiley:

mattm,

Thanks for your post. It was very informative, and I wanted to follow up something you said with my own anecdote.

If I read it right, your advice about the way to select a HVAC system is solid. I went through the process of replacing a very expensive AC unit last summer, and the guy I finally hired sold me on a Goodman. I had never heard of Goodman before and was skeptical. I did some research, but I knew no one personally who owned a Goodman, and I had no idea as to the quality of the brand.

He is a huge fan of the company (I have no idea when the merger that you are referring to took place… before or after my fix), however he said he could install any system I wanted… And he would do exactly that (he gave me 3 estimates with 3 different brands, one being Goodman). But in his educated opinion, it is the installation that makes or breaks the system. He loves Goodman because of their warranty and his history with the hundreds of units he has installed, and he assured me that in his experience they have no more of a failure rate than any of the big name companies out there (like Trane, for example).

For someone like me, who has never given much thought to the HVAC units in my home until I HAD to (they were installed prior to my buying the home, so I had no choice in the system, brands, or installer), the only way to get info quickly is to read reviews on the web from sources like Consumer Reports, and message boards that discuss this topic in particular.

He teaches at the local vo-tech, and he said he has installed Goodman’s on his home.

Before I hired him, I checked his references, and they were impeccable. When he left, I felt very good about my decision. He gave me his home number, his cell number, and his e-mail, and told me I could contact him whenever I needed to if I have any problem with the system, 24/7. He spent all day here, and explained everything he was doing, why he was doing it, and where installations go bad.

Will my system last longer than a more expensive unit? Who knows… But I DID feel like I had the best person I could have found locally to install the correct system for my house.

11

Should I be worried that I knew *exactly *which xkcd before I clicked the link?

12

That’d be my guess. A few years back I fixed mine temporarily by scrubbing it with some steel wool - long enough to get a new one and install it myself.

Nope - I’m not :smiley:

Yes!