Gas Furnace Turning Off? Here's What Might Be Happening

Best HVAC video I’ve seen, you couldn’t have explained it any better. Thank you.

Thanks Tad, you're very thorough and that is why you found the cracked heat exchanger, too bad for the customer but good for their health and safety, they were lucky to have you as a service tech.

This was one of those that start out small but cost the customer dearly in the end. You did save the customers and families life. Finding that heat exchanger full of cracks , praise the Lord. Hallelujah.😊😊

Very informative and well done video. All the right talking points. I learned a lot. Having come from an Industrial HVAC background, I feel that I have a lot to learn in the residential/commercial sector where I now own a business. This was very helpful. Walla Walla Washington.

good Job guys, I am an HVAC tech with few years of experience and i just came accross your video out of bordom amd wanted to appreciate what you are doing, keep it up

I'm about to get out of medical and back into HVAC. I'm addicted to this channel

I have a furnace with 140 limit switch open, now I can believe it is a cracked heat exchanger. I was speaking with co worker over phone and found it. Thanks for the info.

Man you took me to school.
I'm having the exact issue with my furnace. Feel there's a obstruction, but never would've thought about the heat exchanger. Thumbs Up

Man, I like and enjoy very much your teaching scenarios, and troubleshooting a lot. I do HVAC but not like you residential/commercial. I only do apartments complex and pretty much is the same each day, since is the same property. Every once an awhile I do City Residential. But definitely I'm learning and keep learning by watching your videos. You're the best!

Thank you so much for this. I live in Iowa and we recently had 100 degree weather and my ac went out. Now the heat has passed ive found this and after replacing multiple parts (one was actually broken) this helped me truly troubleshoot and confirm. People like you posting these educational videos are real heros to people like me struggling to get by and unable to afford to hire someone.

Customer here. Nice video, i love learning how things work.

Hello, thank you so much for taking a time to make these videos. I learned so much from your videos. God bless you!!!
Toronto, Canada

Your video was amazing from start to scratch, well explained, i bet you a camera scope would not find that crack, hard to find cracks with a camera, but you did everything the right way, good job!

A better filter will keep those heat exchangers clean!! 😊 I’ve been doing HVAC for 17 years, I’m located in Eastern middle Tennessee. You make really great videos! Keep it up!!

You explained that very well and a lot of helpful information for young technicians learning the trade. My name is Eric and im watching your videos from Baltimore Maryland.

Awesome video. I’m gonna rewatch and take notes. I’m an hvac student in Florida and I am confused about direction but you helped me with information thank you.

No better in the business than ol Tadd. He's a master!

Very informative, didn't realize that there was so much involved. Looks like keeping the coils clean is important. Thanks.👍

I did learn quite a lot from this video. I'm not a pro, but I can usually fix things with the right research, and you just provided some no-nonsense information that's gonna save me a ton of cash. Thank you.

That secondary heat exchanger was clean af bro.

My boss and the customers think I should be able to do all this in like 20 minutes, by myself in a cramped attic space. lol You pretty knowledgeable tech Taddy. love your vids.

Very informative. I had 4 servicemen in to see my furnace (100k btu two stage hi efficiency) and had the gas rate reduced, thermostat changed, intake vents blocked off and finally the limit switch changed. About to replace a 9 year furnace. This looks like the most plausible reason since ducts haven't been cleaned in over 20 years!! Thanks

I learned a lot from this video. The biggest thing is the way to check in the limit switch is open with the thermistor, thought that it was only used to find super heats

Thank you.
AC coil was plugged.
Switch was doing its job.

dam thats a big ass crack. i always put a box for 3.5 ton ac or anything at a 100kbtu and over. you offered to fix first before replacment. i beleive in building value with the client. when they see you actually care they will throw whatever you offer them. good work. im from illinois lol

Best HVAC video I’ve seen, you couldn’t have explained it any better. Thank you.

Failed heat exchanger and a fist bump hahah, can't imagine why 😂 Good work guys.

Such a good diagnostics test/learning video. IM SUPER EXCITED

Sir, that was just about the most helpful vids I have seen in a loooong time. Thank you. Saved me a world of headache. BTW I love those Maxi Flex gloves - all I've been using.

Ah man. Thank you so much for this video. My problem exactly for several years. Hidden filters were plugged. explains why the garage was warm. It was pushing against the blocked filter into the garage and cutting out after two minutes.

it was very important for my education, thanks for your time from Chicago IL.

Thanks, you helped me to solve a problem when 4 other technicians before me can't find.

I had a bad limit the other day. It was on a package unit though so it got corroded. Great video once again!

I've been doing this for about about 20 years or more and I always add to returns to the big 90s like that. That dirty coil also could have contributed to that bad exchanger. But I would have never probably caught that without breaking it down myself because it had a rich nice blue and white Flame. In my experience over the years usually when that boy cracks I get some orange in the flame. Thanks for the tips I'll add this in my notes of troubleshooting. Love your content you do an awesome job peace and blessings😂

Tad, you guys in Tennessee really know your ac/heating trade. im glad i follow you bc even tho ive been doing this for 22 years in Fl so no gas furnaces much, i learn something new from you each and every time, cause and effect! Thanks for sharing.

great work and thank you, i am visiting you from Atlanta Ga. keep helping me be a more proficient technician

Great job explaining all the details, Tad!!
You are a Natural Teacher; I’m impressed.
And now I’m off to see if I can figure why my furnace turns on for 30 seconds and shuts down.
Thank You, Kindly, Tad.🙏🏼

Nice troubleshooting & nice find on the heat exchanger ... Good info Tad ... Thx

This was an awesome video!! I learned more here than I have in 6 months of school. Thank you Tad!!

Considering the space above the units most of the time, i never understand why not lift the unit up and take return from the bottom as well. Good catch on that HX

Hello sir. Just want to say I'm new to your channel and the content you present is excellent!!!!! Great Job!!

Great job bro Pedro from Tampa FL leading every time with U.

#1 hvac guy on RUclips. Enjoy these videos dude.

I've just recently noticed an error code regarding the main limit on my furnace, and this video is amazing, will be referencing this video as I do my own testing for sure

Your attention to detail caught my attention while researching some troubleshooting. Keep providing, they're great!

The best HVAC guy

Your videos are liquid gold!!!!! Ty bud

DUDE YOUR THE MAN, Jan 1, 7 am, 58° in the house. What a way to start a new year. I have several furry animals so I change my filter the 1st of every month. Just so happens I used the last one in the case. It must have been in Nov so I missed Decembers filter. Shut main power, would kick on four 4/5 min, then Shut off. Had no idea lack of air flow would kick it off by being to hot. By the way everything was clean in the furnace with all new A/C 6 months ago, new inducer 1 month ago. Thank you so much for making this video. Have a Prosperous and Happy New Year.

Chandler, Arizona its like I'm there working with you, great stuff. Keep it coming brother. Thanks 😃

DUDE. Thank you for this extremely useful video. Super appreciate you, was able to get my old ass furnace back up and going until a real repair guy came by finding a switch with rusting connectors using your multitool explanation, and deoxidizing the connections! HOORAY

Really great informative video. I'm having an issue with my garage furnace my cousin sent me this link. I'm a plumber in illinois. The garage heaters a lot different it's one of those ceiling hung units. I changed the limit switch thinking that was the issue. It's not. I'm going to run some tests and check out the coil but this thing just keeps on shutting off on me. I was also going to try and change the thermostat. This thing was working fine and then it just started shutting off after 5 minutes of operation.

Wow, fascinating. I've actually ran onto quite a few bad limits switches though for some reason.

I LIKE YOUR VIDEO, I 'M LEARNING A LOT FROM YOU THANKS, HI FROM CHICAGO IL.

Thanks for posting this video I’m new to field and need these to learn I’m going to be paying for more details again thanks

I do what you do but I just pull one screw out of limit then stick my “k” type thermometer through that. Or pull limit, foil tape, then poke thermometer through. 😅 100 ways to skin a cat🤷🏼‍♂️ I’m in year 3 an always refer to your videos, thanks for helping us all out🤘🥃

That was impressive diagnosis... Well done. Still scary though, fearing mine will dump out on me..

Thank you TAc I didn’t know you couldn’t add another return at the furnace if there is a water heater near by.

I only service "old school" large industrial boilers. I just had a friend recommended your videos because he knows I love to learn. I wouldn't be working on condensing units, but I loved your video. Like you mentioned, I always want to know what caused a failure to happen so it doesn't repeat it self. Keep up the good work!

Great video, especially the cold air return tip.

That's a costumers are looking an a Technician a true if not the good one but find the heat exchanger a crack that saves the family life but at the end it costly damage to the pocket but money is money life is important. I'm retired but still looking to learn something good. From Toronto Canada good job Taddy. Keep up the good work to help costumers.

Good job on the video,. You missed the leaking and not properly assemble venting, you can tell by the brown stain for the leak and the missing bead on the joints. FYI all those ICP furnaces are either cracked in that location are will have cracked rings on the smooth side in the stainless models. You can reach in through the evap coil cover and feal them with your fingers. For future call you might have you can do a static pressure check across the furnace. This will indicate the lack of air flow. As for the secondary, it was dirty but not the cause of the limit problem. I blame the shit ductwork for that.

Great service brother,good job 💯

Tad is my hero. I've said it before and I'll say it now and Mañana too. 😊 good work Tad

I learned not fist bump when I find a broken heat exchanger. But also thank you, great video.

Great video!!, from duplicating the problem and showing how to diagnose it and then the cause,Thank you for putting this video together. I definitely learned something new. I will now remove my blower and inspect the second burner. You are appreciated Sir.

That so good a really learn something. Thank you for sharing your experience

WOW!!! I learned so much from that video. When I seen the busted exchanger, my wallet started making cash register sounds 😂😂😂 nice video. 👌🏿👍🏿👍🏿👍🏿

Hi ... I am in Everett WA and the video is amazing ... however all i learnt is that i wont be able to fix my furnice but call a technician ...ahahaha... thanks for the video ...

Good video….Really old memory retired building inspector BC Canada. Shouldn’t the unrestricted return air cross section of grilles / plenum / ducts be at least 80 - 90% of the cross section area of the supply air ducts ? Also have to compensate a %age for the return air grilles that restrict the airflow ?
Also badly cracked heat exchangers like this one do leak dangerous carbon dioxide into the house which can make people unwell if not worse.
Oversized forced air systems are bad because they cycle on and off too frequently which stresses the metal and is the main contributor to cracked heat exchangers. Proper sized furnaces will run for less frequent longer cycles which provides more even more comfortable temps.

¡Gracias!

Hmm. If the primary heat exchanger was cracked you should have seen more of a yellow flame within the burners, From what I saw from a quick pass by in the video, they looked a good color of blue. Why quote them on a new unit when you can just change the primary heat exchanger, clean the secondary heat exchanger and then run some new duct? Also you should mention to check the burners and orafices and the roll off sensors. Lastly, if limit sensor was the concern, I would have done a flame test in the tubes to check the heat exchanger and if I saw yellow flame, might have checked gas pressure with a monometer. Good work though and thanks for posting these types of videos. It really helps us all out..

You’re the best. Thanks for the advice. 👍 my name is Bruno I live in Alexandria Virginia

The thermistor was getting hotter then the rating on the limit because it was possibly sticking in to far. That furnace as most Carrier brands use a baffle to direct the air flow directly at the high limit to cool it off. I’d recommend using a piece of tape to hold the thermistor directly on the limit so it sees what the limit does. Nice find on the plugged secondary. Carrier also put out a bulletin for some of there units showing the insulation deteriorating and puffing up inside the primary section of heat exchanger and directly under the high limit the insulation puffs up and blocks a portion of the air from the blower motor even though the baffle is blowing it directly at it, causing nuisance limit trips. Their solution is to remove the limit and cut half-inch strips of metal tape, approximately 4 inches long and put them through the whole of the limit to secure the insulation back to the jacket. No more limit trips. This bulletin is posted and available.Heil is a carrier brand. Great video thanks.

This was super helpful!! Thanks for making!

Bro thank you, for spreading your knowledge u rock. I wanna become a super tech just like u.

I’m Daniel from Chicago, good video hope you make more videos

Well done. It makes me dig a little deeper in my troubleshooting

Hey, if the return was too small then that could definitely have contributed to the short cycling of the heater and a cracked heat exchanger over time. Evap coil could have been dirty too. Good pointers. It's always my last measurement static pressure and too often I wish I would have went straight to it. That man needs a new unit. Good find.

Here from southern Utah. Enjoy your show.

Best video on RUclips! I owe you dinner and a hand shake!

Nice video amigo, I learned a lot about you videos,,,, gracias] thanks I from Chicago I just started HVAC-R business,,

Awesome Tad, you always keep it 200%real !

Outstanding! Perfect dialog! Calm Cool Collected! Thanks Tad! Keep up the good videos!
Casper, Wyoming

Love watching your videos Taddy.

Very interesting video. I like to know how things work and really enjoy watching people who know what they're doing. I can tell within a few minutes if a guys a hack or a pro - You Sir, are a professional.

I learned that the 5 ton needs 2 return. I also like the servicing advice from cleaning the heat exchangers on maintenance. Thanks

Great video with good knowledge. Thanks for sharing

Thanks. I was thinking an appropriate subtitle could be "Discouraging the DIYer from fiddling with a furnace". 🙂
I imagine better air filter(s) would help keep exchanger clean, but that would further restrict air flow making the additional return even more needed.

1140 am thx for your expertise going to take a look at my heat exchanger cabinets for corrosion and leaks❤

Just wanted you to know I followed every test in this video and found the secondary exchanger to be clean. Limit switch was 210 and thermistor showed 250 and if I remove the blower cover portion of the furnace the temp begins to rise past 250 so I have this feeling I’ll have the same outcome but this is now beyond my capabilities and I’m calling in a tech. January has to be the worst time to lose your heat 😢

Maaaaan you really go into Depth your Amazing God Bless Always

Been researching this issue with my payne furnace.
Thank you for this instruction.

Nice job brother I learned a lot from this video

I always sell a high efficiency air cleaner with 90% of my jobs, yes even mobile homes. Saves a whole bunch of service calls.
All you have to do is take a garden hose in through coil area and flush the coil and he out with foaming evaporator coil cleaner and water. Add a pan beneath the blower area to catch the water.

I have the first high eff. furnace from 1985 and its still going strong. I took it apart 2 yrs ago to clean it and the heat exchanger and A coil were spotless. I have a filter of course plus an electrostatic cleaner which must have done their jobs dispite 15 years of dogs.So I would suspect the real reason your furnace failed is poor filtering. BTW my furnace has no circuit board just simple easy to replace sensors etc which is why Im loath to replace it.

lol, at the fist bump on the cracked heatexchanger! make that money $$$ great video!

Great video. You explained everything just fine. Thanks!

Very good video, excellent explanation on primary, secondary heat exchanger and visually shown crack on heat exchanger.

I remember yrs back ac kept freezing up with clean evaporator it was the secondary heat exchanger

I think you nailed it. However, if the return wasn’t that small, the secondary heat would’ve not tripped the limit. It’s dirty but not plugged. Thoughts? 💭