Troubleshooting the limit switch on the 80% AFUE gas furnace
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- Опубликовано: 27 окт 2012
- A guide to determining if the limit has failed and if so why.
This video is part of the heating and cooling series of training videos made to accompany my websites: www.graycoolingman.com and www.grayfurnaceman.com to pass on what I have learned in many years of service and repair. If you have suggestions or comments they are welcome.
If you are a homeowner looking to repair your own appliance, understand that the voltages can be lethal, the fuels are highly flammable and high pressures are used. Know your limits. 
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Temps hit 24, house almost freezing, no companies available to come out today, your video saved our pipes from freezing. a small tap and we were back working again. Thank You grayfurnaceman
One flick to the limit switch and my house is warm for the night! Two kids are taking their sweaters off now. Thank you. I’ll replace the switch tomorrow.
Thank you for posting this excellent video. $20 limit switch later, and my furnace is up and running like a champ. This video saved me hundreds in repair service.
Fantastic video! It solved my problem, during the coldest night of the year so far, near zero. I called 8 or 9 heating repair guys, and none had the time to help. Thank you very much, and my new part is on order, and I will now have heat until it arrives, thanks to you.
Thank you sir! I was searching for a fix to my furnace problem and this was it. Your video saved me a call to the HVAC guy, a cold night, and probably a few hundred dollars!
Coldest weather in decades around here, and of course the furnace stops blowing cold air. This saved me a cold night, a huge hassle, and a fortune with the HVAC guy. Thanks!
I reviewed several videos and out of them all this one was by far the most helpful. My Trane furnace was blowing cold air. I finally got it to light after I removed the limit heat switch, smacked it a few times and replaced it as was done in this video. I also ordered a new replacement limit switch as was also suggested here. Thank you very much!!!
+John Tessler Welcome
GFM
Thanks a bunch. 2 in the morning, and my furnace is not heating the house. Looked at the trouble code..33. Look at the roll out switch with a junkie voltmeter and it appeared to be fine. Looked at a few videos which pointed to the limiter switch also. Then watched your video after I pulled it and you said to flick it which I have done in the past on other things that have stuck open. But since I don't know much about furnaces you basically rattled some sense back into my head. And yes it worked and my furnace is up and running again. Thanks! Getting a replacement part today. Oh yea, and I effed up because I let my filter get clogged up...I've been busy....
i love it when good ole youtube saves me a service call...Thanks grayfurnaceman...totally bang on!!!
Thank you sir! You just saved my family from having a really cold night! It's about -7 outside and after pulling the limit switch, hooking it up to my meter it was an easy step by step fix. Also, thank God for my wife's small hands- she was able to pop the screws off and on. You rock!
Merry Christmas
GFM
thanks this video got me through a really cold day, saved me at least $50 cause I ddnt have to call a hvac company, gave me time to order the limiter switch and install myself
+Gi Baseline Welcome
GFM
Again, a Very good Vieo! Just had a call like this on friday. too funny. credit card limit open. 140-30. guardian furnace. 4 years old. dirty filter and customer closed off 2 registers downstairs. drywalled over them. i told him to open them back up. not enough air flow for a 4 ton furnace. 100,000 btu. it only has 4 mains and 2 bath. he closed off 2 mains. gotta love those engineer homeowners from boeing. and he's a real engineer and should know better.
You're a genius. Thank you so so so so so much for this. I was able to fix our furnace and get the heat working again today. I felt like a total champ! The repair man still came by to check to see if everything was ok, but that fee was a lot less than what it could have been. THANK YOU!!
Welcome
GFM
Thank you so much for the info. Save us today coldest day so far and a Sunday evening not wanting to call for emergency repair. We pulled the limit switch flicked a couple times got us back up and running for tonight. Will pick up a new switch tomorrow. Thanks again
grayfurnaceman---Thank you VERY MUCH! Last night it was close to 0F outside and I woke up to a room at 50F and the HVAC blowing cold air. The thermostat was set to 68F, but there was no heat, no flames in the furnace and just a blower fan that kept on spinning. I called in an HVAC guy who told me I'd need to spend $6,000 to replace the entire heat pump unit. I did some research, talked to some people, and bought a replacement ignitor. That didn't fix it. Tonight I watched about 15 videos on RUclips and pored through the Goodman technical documents---anything to avoid paying $6,000 to fund the HVAC guy's boat payments. Nothing helped. The blinking light on the control board told me it was the main limit switch, but none of the info I read actually told me where the switch was located. I was about to give up for the night, then I did one more search and found your video. You described the exact problem I had, and when I pulled the limit switch and tapped it a couple of times, replaced it, and switched on the furnace, it fired up within 20 seconds!
The only issue I have is that the limit switch cannot be removed entirely because the gas pipe and valve are right in front of it, blocking its removal because of how long the probe is. I really want to replace the limit switch to avoid a repeat of this problem, but I can't get it out. The thing came out far enough for me to tap it firmly, but that's it. The video doesn't actually show how you got it out---at 3:35 it's installed, at 3:36 you've removed it.
He said the limit switch indicates there is a problem somewhere that needs to be fixed and he mention do not just replace the limit switch . so since you got it working did you have to fix anything other than the limit switch?
You have my sympathy. I have a crappy Goodman furnace as well😞 Fortunately my problem was a rollout switch which is quite easy to replace. Also living in Southern California lack of heat is a mild inconvenience.
@@adamhanne8431 Thanks Adam. You are right, appreciate the advice. I've observed the flames (for a long time) and they are all burning straight and true. It's been over 9 days since it tripped. If the same switch trips again I could just replace it but I will probably call a technician. My bet is a flue blockage but it seems to be evacuating OK.
Thanks so much for expert advice, given with a generosity of heart, and excellent technical process. You explained clearly, not using sophisticated tech-speak, and you worked that camera to show what needed to be seen. Again, thanks for sharing your knowledge freely and graciously. Blessings and peace be upon you and yours.
Thanks! I paid someone 150 last time I forgot to change my filter and did myself this time with your help!
Thank you so much for posting this. Had the same problem during one of the coldest night in Toronto. Fixed it following the video.
I couldn't believe it when I gave mine a little thump and got a low ohm reading on the multimeter. Problem resolved. I appreciate the time you took to make and upload this video.
You are probably not done. If it sticks once, it will stick again. Replace it.
GFM
Another clearly explained video that helped me located the source of the problem: a sticky limit switch. Thank you.
Wake up at 3 A.M. fan running all night cold air. This video helped me fix it......Thank you so much for posting this......$$$$$$$Saver
Thanks to your lesson on the limit switch, I was able to get my furnace working again. The fan just kept running but it wouldn't ignite. Once I removed the switch panel and exposed the switch, I have it a few taps, put it back in and flipped the breaker and the ignite light came on and, after a few minutes, we had heat. I will replace it as you suggested. Funny, though, it was taped to the probe so I am not sure how I will get the new one attached. Very, very much appreciated!!
Thank you, thank you, thank you. Your videos are by far the most helpful thing when it comes to furnaces. You helped me out last year when it was the hot start igniter ($60 instead of $300 to have someone look at it) and this year again - when it was the limit switch. Tapped it and it's working again (and yes I checked the rollout switches first, thanks for that important safety tip). Thanks to you we haven't sat around helplessly waiting for someone to come fix a simple problem. I think my landlord's thankful as well, since he paid me back the $60 for the hot start igniter last year. :) Now to go order a limit switch...
+werwerwe Welcome
GFM
You're the best! Knowledgeable. Great lighting, camera work, narration. Clearly a pro. Thanks!
Your advice fixed mine. I just remove the limit switch and flicked it a few times, reinstalled and works now. Order new switch.
Glad you got it going.
GFM
How did you remove the switch from behind the gad box?
Bless you for posting this video! After checking the hot surface ignitor, clearing the drain pipes, and changing the filter I wasn't sure what to do. I eventually found the limit switch and it had zero continuity, then I flicked it and it worked again. We'll be ordering a new switch. Thank you!!
garfodie81 Welcome
GFM
You just saved my family from a very cold night here in Denver. Thank you.
Its good to be warm.
GFM
I encourage you to do so. When I was teaching, I had to pull someone off a unit most years because he was afraid to lose the refrigerant. By the way, tight fitting gloves are a bad idea, as they get saturated with refrigerant and continue the burn until they can be removed. Thanks for the comment.
GFM
Thank you from the bottom of our frozen hearts! Excellent video and explanation, so helpful!
I had the problem of fan keep running! I fixed it by this great explanation, I learned much!. THANK YOU VERY MUCH . GOD BLESS YOU!
Helped me to quickly diagnose the problem and resolve it. This video saved me a money as I can replace the part myself vs having a service call. Awesome. Thank you Gary!!
Welcome
GFM
Excellent explanation. I appreciate you took the time to make this video many years ago.
THANKS!! Saved my family from freezing tonight!
You sir are a genius. Perhaps the best explanation for a limit switch on you tube. I did the same thing by tapping it and it worked. But I did order a new one if it fails. In my case the limit switch keep the blower on after the heat was turned off.
That is as it should be. If the limit sticks closed, the furnace thinks the unit is overheated so it leaves the fan on.
GFM
Thanks for the Help. This has truly been a blessing to me
thanks so much for making these videos this one saved me from calling in someone!
You are the best Grey! Keep em' coming!
Thanks a ton! Furnace here is now back and running.
Thanks for the support.
GFM
If you have a manual reset rollout limit, you can reset it by pushing the button. I just did a vid on rollout switches. You might check it out. I am not sure where you would find the rollout switch on that unit. It should be located above and close to the burners. You need to find out why it has shut off. Could be cracked heat exchanger, plugged ht exchanger. If the limit shows continuity, it has not failed. Good luck
GFM
Great information, though this is pretty advanced stuff for me to fix. Looks like I need a trained technician. Good to see the nuts and bolts of a furnace explained.
Better to handle the limit problem yourself. If it is the roll-out call someone. Because that could signify it is not a small part at fault. but something expensive and seriously unsafe. Furnaces are very simple devices with similar orders of operation over every model. You can get a meter for the price of calling a tech.
In almost all cases fan running with no heat screams open limit.
The limit is probably stuck off or there is a manual reset limit off. It is usually located behind the gas valve. On the vid you can see the left edge of it behind the gas valve. Turn off the power and remove the limit then tap it on the switch. It will probably come on. It still needs to be replaced. Do not bypass!! Hope this helps.
GFM
This video was exactly my problem! Ordering a replacement limit next. Thank you sir!
Welcome
GFM
Thanks so much!! We got home from Christmas Vacation and the furnace wasn't heating. This got us going again..
I love the flick tip at 4m 25s. Thanks for saving me!
+Dave Van Allen Welcome
GFM
Very informative to me. Very well put. Learned something... glad to spend the 8:38 +.
Good video,great practical approach to showing real life troubleshooting.
I thought it is a great video, lots of good information...
Honeywell switch
Thanks for this very helpful video, You nailed my repair! You are the BOSS!
+e-biker x Welcome
GFM
Wow that must have been some burn. Here's hoping for a return soon to the biz. I bet you could do some good vids on refrigerant safety! Take care.
GFM
Thank you! Worked perfectly.
Thanks for that . I have no knowledge on this stuff. That’s gold.
Welcome
GFM
This was very good information. It helped me put heat back in the house until I could get a heating guy to my home to fix the issue. TYVM!!
This video helped me tremendously!!!!!! Thank you for taking the time to make it and help us save a hundred/s of dollars!! So said my husband.
Welcome
GFM
Thanks so much, was able to tap on my limit switch and get it back on hopefully will hold till I get the new one!
+territodude Its nice to have heat.
GFM
I would be looking for a blocked or cracked heat exchanger. Even though it does not look like it, it probably is rolling out. Place your hand close to the burners to see if heat rolls out. The other possibility is if there is a negative pressure in the room the furnace is in. (exhaust fan, dryer, etc). Hope this helps.
GFM
Thank you, took me a little while to get to your video. HVAC tech said circuit board failed however LED code = 33 which led me to limit switches and hence your video. Switch stuck open, replaced switch.. fixed. haha still need a new furance and AC unit soon though :(
LagrangePoint Welcome
GFM
you rock. . a little tap and I was back on the warmth. . you explain wonderfully. . THANK YOU
+Susana Matos Be sure you order a new switch so it does not happen again.
GFM
grayfurnaceman thanks. . Will do! !!
It should not. However, if the flame shuts off within the trial for ignition period, it is probably not sensing flame. Have you cleaned the flame rod?
The only other solutions I can think of are a bad control board or the possibility of a heat exchanger crack near the limit switch. Try temporarily bypassing the limit. Do not leave it bypassed!
GFM
Thank you for the video, got our furnace working again :)
GAL Glad it helpedGFM
Grayfurnaceman: as a retired HVAC mechanic I cannot count the number of times I encountered what you are saying about clean/dirty air filters starving the return for air. And as you say the furnace runs too hot and kicks off on limit. The over temp limit is doing its job. In some homes I would find a central return grille that the homeowner has blocked with a piece of furniture or a rug, and they get this condition. The furnace has to breathe just like you & me.
Thank you for posting this video! It helped us fix our furnace.
Merry Christmas
GFM
The dial should be set on 200. That is the very bottom position. The wires on the limit switch should be removed before checking with the meter. If the meter reads OL the limit is open (tripped). If it reads 3 or less, it is closed (working). Hope this helps.
GFM
thank you for the insight and the importance of using the right part for the fix and explaining why there in place and their functions god bless
Merry Christmas
GFM
Thank you so much for your video I found your instructions the most helpful and I was able to resolve the problem with my furnace as you recommended in your video I am going to purchase a new one to replace the part Thank you.
Welcome
GFM
Newly subscribed, I luv ur style of teaching. I'm learning a lot keep it up.
Thanks for the valuable information you've shared,very clear and useful...cheers!
Welcome
GFM
This video was a life saver!!!
You are quite welcome
GFM
Thanks for the great video. Saved me a service call.
So true. If a limit switch is bad, you better find out why. They don't break for no reason. The furnace has been overheating.
Thank you so much for explanation. You took your time to explain it. God bless you.
Thanks
GFM
Thank you. Good info on the filters it makes sense.
Welcome
GFM
Hey man, different furnace but this helped so much. Gave the thing a whack, lit back up. Usually these whacks are out of anger hahaha.
You saved me a bunch of money. Thank you sir!
Welcome
GFM
Good video Thanks! , I learned something new!!!
great video as always!
Quick question GFM,
So far the last few days I've been having a frustrating problem with my furnace. Once the desired set temperature is reached in the house, instead of the heater just shutting off, the hot air stops coming and only cold air starts to come out of the vents. The hot air always stops coming out once the set temperature is reached. This leaves us with the fan constantly blowing.
I have never had this issue before so it couldn't be the thermostat wiring, so I figured maybe I had a faulty thermostat. I replaced the thermostat with a new unit, and I still had the same issue. So i'm ruling out that the thermostat is not the culprit.
After doing quite a bit of research online I have came to the conclusion that the limit switch could be the problem. In your expert opinion would it be wise to swap out the limit switch or should I try something else first?
By the way to note, the furnace is a gas unit, with an electric pilot. I had also changed the extremely dirty old filter out about 2 months ago.
Any help would be appreciated!
It is a fine soldering job. You can try. Maybe you win or maybe you lose. Hope this helps.
GFM
very helpful video,i love these gas furn videos,this is something i dont get to work on very much,i have had to change some inducer motors/blower wheels and a few gas valves,ive worked on several after thinking about it,but not as often as i would like,i am out of work do to frostbite to my hands from R-22,Dec.29 makes 1yr out now,and still not getting any good news yet about my rht hand,got it bit bad,but the vids on ytube and reading a lot help me keep up,i hoping to get back asap,may be awile
I do service work and fix most of my own things but I missed this completely. I just dragged my filter out of my York furnace and like magic no more four red flashes. The enclosure for the "A" cooling frame does not get too hot to touch now. It must have been borderline for at least three years. Thanks!
Great tutorial!!
Thanks for the great info! I removed this switch while I was troubleshooting a flame sensor fault. Found the cover of the switch had fallen off in the plenum. Could this give the appearance of a flame sensor fault?
I would guess there is an airflow problem, or the unit is overfired. If filters and blower wheel are clean, and its a high efficiency unit, check the secondary heat exchanger. It's also possible the ductwork is restrictive. Hope this helps.
GFM
This sounds like a problem with low voltage wiring. Start by disconnecting the Wire going to W at the board and proceed until you find the problem. Hope this helps.
GFM
Thank you ...you saved me from going out on a snowy night
Welcome
GFM
We are looking at the flame sensor. Checkout "How does the gas furnace flame rod work." If it is not shorted to ground and the wires are tight, it is probably a board problem.
GFM
Thank you, Thank you......sooooo much for posting this Great video...
A million thanks 2 u. This was right on point for me.
Welcome
GFM
thank you very much God Bless you
Exactly! Reusing that thing has callback written all over it. The boss hates callbacks.
OK, lets start over. If the burners come on then shut off within 7 seconds, it has a flame proving problem. If you have a meter with microamps, you can check the microamps. Most will prove at .5 microamps. If you dont have that meter, check the sensor, after isolating it, with an ohmmeter to chassis. Should be open.
If burners run for 2-3 min, with room temp set higher than room temp, there is not enough air or the heat ex is cracked near the temp probe.
GFM
Thanks very much sir. Just one comment - and maybe my ears are bad :) but I found it had to tell sometimes if you were saying OFF or ON - they can sound kinda similar, and for me, it was hard to tell for sure a couple times which one you actually said. Just my two cents. But thanks again, much appreciated.
Thanks for the video. Very helpful you saved me a lot if money
Welcome
GFM
Good to know thanks again!!!
Thank you very much! the flick fix worked, You mentioned replacing with factory parts. Where can you recommend finding factory replacement parts?
liked your video, very helpful but I was a little surprised when I looked at my Limit Switch and the temp number was L290-30 it seemed a little hot for a 100,000 BTU Bryant, got me wondering what would happen if this was replaced with wrong temp limit switch?
I did clean the rod once before and it worked fine for a while, I'll try bypassing the limit switch tonight, about the test with the flame rod I couldnt test it because the flame doesnt stay on for me to touch it to the chassis. I ordered a flame rod since it went bad before, i figure I'll replace it for a new one. do you have a vid about a cracked heat exchanger?
Thanks GFM. One of my rollout switches kicked off and I reset it. I have a couple of spares in reserve and so far it has not kicked off again. I had a new roof installed recently and there may be an issue with the flue but I haven't found anything. So far all is well but I am still concerned. If it happens again I will replace switch and see what happens. Any advice?