Nest Thermostat No Common Wire- PROBLEM SOLVED -How To Install Nest Missing Common "C" Wire 

Hook It Up, I just purchased the E thermostat and was also running into the four wire, no power issue. Found your video to be extremely helpful. Moved the blue fan to C and moved it to C on the circuit board. Power charging the device and now there are no issues. Nice editing and comedy in your video. Respect and now a FBM.

YOU ARE THE BEST!!!!!!!! i wish i could like this vid 1000000 times. fortunately I had an extra blue wire ran to the furnace that was already hooked up to the furnace, but there was no C connection, it was connected to B which was labeled as 24com. I did a half assed google on "B 24com"and concluded it was the common hookup. now my nest is getting a 200ma constant charge, which is higher than the 100ma charge I heard someone else report, never the less it is finally functioning as advertised. thank you again, i have been so frustrated about this the past 24hrs. I am going to link this video to the nest reviews on amazon now to help everyone else out.

Thank you! I have a 4 wire system and my nest kept dying but now switching the common green like you said....viola!! You know more than nest tech support does.

Thank GOD for this video! I have been on the phone with Nest for a combined 3 hours and had two technicians come out paying $250.00 total. Both wanted to run a new line with 5 wires. I have 3 nests and we would have had to cut sheetrock all over to do this. NOT AN OPTION FOR ME. I had to call the last tech back out and make him watch the video. THAT WAS A CHALLENGE! After watching the video, i was up and running in ten minutes. THANK YOU SO MUCH!!!!!!

I'm pumped now. I pulled my thermostat and saw 4 wires, but then a blue wire tucked away. I went to the furnace and see it is connected. So I have 5 wires. I have a C wire. Now I will for sure get a nest. After doing a little searching, I see people have problems with no common wire with the smart stats, so glad I gained a little knowledge from this video and from other sites just knowing about the constant power a smart stat needs.

This helped tremendously. I spent 2 hours in an on-line chat session with nest. I had a 2-wire system attached to an 1960 something thermostat with the mercury bulb. Nest told me that the thermostat was not compatible and that I would need to hire a contractor. Did some research and found that I needed a new wire allowing me to have a "common wire" to supply a consistent low-level stream of electricity to my nest. I threaded the new wire thought the wall and to my furnace, followed the wiring instructions in this video and everything is working perfectly. Nest support sucks, but don't give up. If I can do this, anyone can.

1) Bought a Nest Thermostat for my new home. 2) Took a picture of old thermostat wire configuration. 3) Got the wall plate and base and started working on that. 4) Installed wires on the base based on configuration of old thermostat. 5) Got Nest to work. (Yay) 6) Left new home to sleep in old one. 7) Came back to find Nest lost power. 8) Freaked out. 9) Begin troubleshooting the issue. 10) Found that Nest was below 3.6V 11) Found that I needed to install a "common wire." 12) Freaked out more since I am not an HVAC technician/electrician by trade. 13) Googled some more to see if there was an alternative. 14) Found this video. 15) Took many deep breaths as I was about to go into my furnace. Turned off power to furnace on the breaker box. 16) Found control board with the letters clearly under the wires/grounding screws. 17) Took my trusty screwdriver and switched the G and C cables (after I had moved G to C on Nest) 18) Turned power back on. 19) Ran to the Nest Thermostat. 20) When to Settings>Technical Info>Power and saw battery voltage was climbing up. 21) Breathed many sighs of relief! Almost spent $100 on a Nest Pro! Thank you for this video kind sir!

Had the HVAC guy out here, even called NEST/Google - told me I had to put the old thermostat on or just do without A/C. The bypass worked like a charm!! Appreciate the tip!

We had a R Y W and G. The nest caused our furnace to short cycle, turning on and off. We didn't have a C common wire. Nest support couldn't help and told us to exchange our Nest. We tried that. We also tried charging it with the USB overnight because forums led us to believe it was a power problem. Tried this and it worked! It was our last ditch effort before taking it back to the store, so thanks!

Thank you! I was messing around lastnight for hours trying to get it to work. I called nest and they told me it's not compatible with my condo hvac. I spoke with my brother who said it's probably a common wire issue but he didn't have time to come and look at it. Your video solved my problem!

Oh man thank you so much. My Nest Thermostat E would run the fan all the time even if the thermostat was off. Spent an hour with Nest on the phone and nothing. They concluded that my base plate was bad lol. I don't know anything about A/C but I could tell that was not the problem. Came across your video. Thank you so much for explaining the function of the green cable. I switch the cable to be a common wire and problem solved.

I've had the Nest thermostat for about a year and have not had a problem with it until the other morning when I woke up and it was 45 degrees in the house. The Nest lost power at 3 a.m. I pulled it off of the wall and pushed it back in and it worked, but would not connect to Wifi due to the battery no longer charging. I pulled the Green wire out of the G in the Nest as well as the furnace, and put it in the C (common wire). It now works great and it is fully charged. Thanks for posting this!!!

Super helpful! I previously had a technician come out who told me that the unit needed a common wire. I don't know why he didn't install one. The video simply and clearly explained how to fix the problem. I'm not all that handy, but I can follow directions. My place is finally warm. Thanks!

Just purchased a new Sensi Touch screen WiFi Thermostat and my Rheem AC Unit has 4 wires only. After watching this great video I now have a fully functioning system with this G to C Wire swap. Thanks for posting this. 2 thumbs up

It just AMAZES me that I can find almost anything on Google ... I bought the Nest Thermostat ... and after installing it was useless ... I went through the Nest Troubleshooting apparatus ... even called to speak to a Tech ... They were no help at all. So I Googled NEST THERMOSTAT PROBLEM ... and I got this hit . After two weeks of trying every imaginable fix ... It took ten minutes to do The Common Wire fix as described here and BAM ... it works perfectly

Great video, thank you very much!!! I was about to purchase a new Nest thermostat because of the battery discharge issue when I found it. Did the G to C swap both in the thermostat base and in the furnace exactly as it is in the video (1:25 - 1:50) and it worked like a charm - the battery is fully charged now. My only suggestion will be to add "solving the battery issue" somewhere in the video title for people who are not aware that the missing common wire is causing the battery discharge when the thermostat gets older.

This video was extremely helpful. It solved my Nest issue with the heat not coming on due to no common wire. I switched the G wire to the C connector on the Nest, and bam! No more annoying fan control and now my heat works properly. Thank you!

Perfect, Thank you so much for this video, my nest was turning the heat on and off and then restarting, always happens in the middle of the night, called nest and they said I needed a common wire ran from my furnace all the way directly to the nest, I switched this wire as you showed and it worked great !!!!, Thank You SOOOO Much !

THIS VIDEO SAVED ME !!! Here it is YEARS later and it is still helping us THANK YOU ...

IT WORKED!!! You're the best, man! My Nest thermostat needed a common wire, so I used the green wire as you suggested. Worked perfectly!!! And you're right - the fan went on and off as it should. A local Nest PRO wanted to charge me a minimum of $300 to fix it. I just fixed it myself for free, thanks to you! THANK YOU!!!

Man, thank you so much! My sys actually had a blue common wire. But every time I put it on, the Nest would NOT even start. So I would run it without the common wire, and the system would continually kick off when it needed more power. Before I made the green wire switch, my power numbers were Voc:36.77 Vin:25.63 Lin:20mA. After switching the green wire, Voc:34.73 Vin:34.73 and Lin:200mA. It made all the difference in the world. It is now running properly, and I really appreciate it. I doubt I will need anything else from your channel, but have subscribed anyway just to help you out for those who do. Thanks again!

I didn't even know having more than four wires was a thing, I opened my furnace and saw 4 unused wires, the blue wire got elected as my 5th wire and now I have a common! Thanks again.

5 years later this video still relevant and helpful. thanks fam.

Thanks man this helped me out 2 years ago to install it. And helped me out today when I swapped it out for a normal thermostat before selling my house. Hope all is well.

Thank you AC wizard, I just did a job last week and after watching your video it works.

thankyou so much, i had the c wire adapter overnighted and still didnt work because I have 2 y cables.. but just switching the green over fixed it and saved me 25$! amzing this video still holds up 8 years later😂

Real nice of NEST to tell me about this video before , I like many others had only 4 wires and I called a contractor who said he was unable to run a common wire to my nest thermostat, I took my nest back to the store , I didn't throw it like you did :-{ . oh well maybe ill try it again if this works.

Man. Just replaced my 20 year old furnace that had a nest on it. New furnace fan ran constant. Allot of hours trying to figure its out. Then came across your video. Worked!!!! Thanks for the help.

Thanks! This morning with temperatures dipped below zero, the Nest had an error code about not getting power and installing a common wire. I was able to move the ground wire to the common wire and all is good once again. Thanks!

Thank you! This was the solution to the e74 error code that my Nest Thermostat was giving me after installation. I called Nest support first and sadly they weren't able to help me at all. So glad I found this video. Once watching it, it took me all of 5 minutes to make the recommended wiring change. My Nest Thermostat is now working properly!

You are the man. This video did the magic for me. Within 10 minuted after this my Nest thermostat started showing 3.9 power from 3.5

Wanted to give thanks to this video! nest worked great for tail end of winter then spring, when started to use AC it would trip every few hrs my breaker. Was about to put old thermostat back on and found this great video. Problem solved added common, worked like a charm! Thanks!!!

My nest was causing my blower to short cycle while the a/c was on. I followed the instructions in this video and now the blower stays on until the a/c turns off. It works perfect and just in time for summer. Thank you!

OMG - this happened to me New Year's Day on Long Island during record cold snap. Had to endure usual HVAC tech complaints of Nest. After heat restored and he left, was ready to run new wiring from thermostat to furnace if it happened again. Thanks for making this video - saved the day, night and New Year's.

You just saved my family a cold night. Thanks a million!

Thanks for taking the time to put this video together. We have two Lennox furnaces and I first came across your instructions when installing the Nest on the upstairs zone. This and installing the Nest took about 20 minutes, (plus the 30 or so minutes of being extra careful I was doing it everything according to your and Nest's instructions). Today I'm stalling the second Nest. Thanks again!

Dude hilariously helpful. I spent >1hr on the phone with Nest that lead to them connecting me to a "Local Pro" who would come snake a new common wire to the thermostat....at my cost. This worked out great, THANK YOU!!

This is a great DIY video. Thank you! I spent hour on phone with Nest Tech Support, which is amazing then elevated to Sr. Support who told me I needed common wire. Luckily, I have a blue wire in bundle; however, I was told I needed Nest Pro to complete installation. Now that I've watched this video, I've got it! Thanks!

Thank you so much for helping me set up my Nest thermostat. I watched several videos for my first generation nest thermostat and then I came across your video. It was so simple. I watched your video once and quickly caught on to what you were saying. I switched one wire on the heater and one wire on the thermostat and I am up and ready to go. Thank you so much for your time.

Thanks for this helpful video! I almost returned my Nest Thermostat thinking it was defective. Nest should pay you for this video!

Thank you! Confirmed fix with my 4 wire system and switching Green to Common both at furnace and on Nest. Thanks for saving me about $200!!

We just installed a new thermal pride OH8 and tried to add the nest but because of the common wire problem system wouldn’t operate correctly and I was thinking I needed another transformer or a jumper wire from jeep to see you solve my problem thank you very much!

Wow... This was a great video.. This guy rocks. It solved my problem with the NEST v3. I have a common wire but it was not connected on both HVAC unit and the thermostat. I had followed the nest instructions but it did not work. As it turns out, my HVAC unit does not work with the power stealing method of the NEST. So, I connected the common on the HVAC and then connected the common on the NEST....BAM... it works now. I had searched the internet and everyone else kept saying you don't need the common

Was having the "delay" issue recently with the onset of very cold weather. Did the G to C wire swap on both the Nest and NEW furnace control board. Issue solved, THANK YOU, but now I have lost the Nest fan control. I used the manual fan control for equalizing house temp in both winter and summer. UPDATE later the same day: Decided to bite the bullet and fished a 5-wire thermostat wire through by soldering it to the old 4-wire. Everything works fine now, AND I have independent fan control as desired.

This is great. Going to try the common wire fix. This thing has been turning the fan on and off every few minutes when I run that ac. I LOVE the nest but I don't want to destroy my furnace.

Thank you so much. I was having trouble with an ecobee3 not having a common wire and the pek was not working correctly with the ac, so I ditched it and put the green wire as the common on both the circuit board and thermostat wirings as you said, and it worked great. You're pure genius!

Sir, I have been looking at your video/issues regarding no C wire and like many, I purchased a Nest Thermostat. This issue is very prevalent on Oahu, these track homes dont usually have the C-Wire for a thermostat, to be fair because in the past we didnt need a C wire for these 20th century mercury-type thermostats, now we do... Just about about 3 months ago we finally installed after 20 years, we replaced our Rheem Central Air Unit up in the attic and the fan module in the back yard. Typically these track homes here, the builders here always put the "minimal" units to these new track homes. Anyway, we have this,"Haus-beast mode Ac Unit" now and it sounds like a jet starting up with all the cool air blowing through our large home, even to our farthest rooms in the home downstairs...nice...Sir, but again we didnt have a C-wire so the new installers weren't able to hook up my Nest Thermostat and just put our old battery thermostat for now. I really was considering your other incredible video with the plug-in transformer but to me sir, having a transformer is just so ghetto(for me) I can do what you illustrate on your other transformer video because it is so simple since I have an outlet just below the thermostat area upstairs but again to me, it just doesn't look good and it takes an outlet socket away from our daily chores and what not.......BUT Honestly Sir....I know i can do this...I just need to go up into the attic and switch out the fan wire(because frankly, for over 20 years NEVER i have used our fan option, no one has on Oahu...) and reroute it onto the C-wire on main unit in the attic and Nest....Im am a RU-vidr advocate repair guy, i too also have some How To Videos to help out. Wish me luck...ill be turning off all the voltage when i make this upgrade..Mahalo...ill let you know...your video looks so painfully easy...Just follow the yellow brick road....Mahalo Again Dana

Great video ! Just to add clarity here the "C" Common wire is needed to supply power to the nest thermostat. So make sure this wire runs to "C" on the furnace circuit board. If you have a thermostat that is battery powered you may not have this extra wire, so you will need to add it..

Thanks so much. Nest support could not figure it out but this certainly did. Worked like a charm. Oddly the thermostat upstairs still uses the fan wire and does not have the same issue, very odd. Same units and everything.

Thanks for the info! I had to rewire my furnace to make it work but I finally got it. I almost took it back to the store glad I watched your video!

Dude... i love you for this video. I had an unused blue wire that i hooked up to a "C" terminal on my furnace and used in on the terminal block for the Nest. You-da-man

Thanks for helping help! You were on point with the common wire problem. No more dropped internet connection and 🔋 power stays at a constant 3.93 volts. I do miss controlling the fan separately, but I barely use that feature.

Thank you! Worked perfectly for my 4-wire Trane furnace/AC. We were on a road trip and Nest app said "offline" - we hurried home with indoor temperature at 41 degrees due to short cycling/low battery. Luckily no pipes had frozen. Was easy to move the green wire under the Nest thermostat to the common wire space, and then moved the green wire to common wire in furnace. Tried to call Nest tech support but went into long queue. (For a quick temporary fix, we just disconnected the yellow wire and the furnace worked).

Have a Nest on order and after watching a different install vid checked my wires and I only have 4. Maybe once I take the old thermostat off I'll have more wires in the wall. I never use just the fan anyways, so this tip will help me a ton if I have to do the wire swap

Great video. Two things... you can now control the fan separately to come on for as little as 15 minutes to 12 hours. Also in the nest box are sticker labels to wrap around the wires so you know where they go.

Awesome! Spot on :) In my installation I used Blue instead of green and labeled it on the thermostat end.

THANK YOU SO MUCH!!!! Fixed my problem and saved me some $ on having a pro come in. The installer never hooked up the common wire b/c the honeywell panel has batteries and a C wire is optional.

Finally, sensible instructions. I moved my green wire to C, problem solved.

Thank you for this video. Im on the fence about a Nest because I don't have a C wire, but this makes me think I should give it a try.

I had an error 103 on wire Y1. Turned out I had made the error #1 and labeled my wires the conventional way instead of the heat pump way. As soon as I wired them the heat pump way, the nest detected the correct devices and stop giving error e103. I was minutes from calling an electrician. Thank a lot!

I just came across this video in doing some homework to install either the Nest or the Ecobee. If I could buy you a beer I would, thank you!

I just spent two hours figuring it out without this video. I wish I had seen this video before I discover I had a common wire but it wasn't hooked up to the furnace circuit board

I subscribe to your channel because of this video. Thanks.

This video was spot on. I did exactly as described and it works perfect now.

I would much rather lose fan function than run another wire from the furnace to the thermostat. Thanks for the tip! Made the switch and no more subwoofers in the attic 😎

thanks man! much appreciated. i'm going to try this. my AC was intermittently turning on and off. had to put my battery powered honeywell back on the wall. i'll look at my furnace for G and connect green wire. i don't need to control the fan, as long as it goes on and off with the nest i'm fine. i see you're in Chicago. me too. beautiful GSD. Our girl is 4 months old.

This fixed my power cycling problem last night! BOOM thanks!

We had a major problem installing the Nest thermostat. We have a two stage furnace that apparently requires special wiring for the Nest. We did not know we had a two stage furnace until I inadvertently blew a fuse in the furnace panel (in the attic). You may have THREE power supply switches to your furnace. You need to turn them all off before you start. We tried to work with Nest and the technician had us shift wires over and over during a one hour period. It was a nightmare of difficulty in handling tiny wiring. Nothing worked. Even the contractor we hired after this debacle was not able to get the Nest to function properly and stop giving error messages. IF YOU ASSUME THAT YOUR FURNACE IS COMPATIBLE WITH NEST YOU MAY BE WRONG. We returned the Nest and put in an Emerson (easy read) thermostat. It works fine and our single story home is very comfortable. Sometimes modern digital equipment is more trouble than it is worth. If you want to install a smart thermostat yourself, or use a contractor who is not a "Nest specialist" you may regret it. Sometimes "simpler" is really better. sanjosemike

Didn't expect to laugh at a HVAC video. I did. Upvote for you.

Thanks for clearing this up, My current Carrier thermostat's Y cable is black, so I'm assuming they used whatever copper wire they had when installing the Furnace. I was worried it was something else.

I never got error like some. For me my fan would trip off and on despite ac still running outside and house not at temp. I opened my panel and noticed I did have a common wire running into walls. I went into attic to hunt it down and saw that it was traveling to compressor outside. I have a narrow truss with fifteen foot ceiling and didn't want to bother running a common so this ended up working like a champ. Spent an hour and thirty minutes on phone and was prepared to return unit until I found this video. System working perfectly now.

I had issue where the HVAC people didn't attach the common wire. But the wires were there. So I just used one of them for the common. :) I had no issues with out a common wire till this morning when my nest had a dead battery. I think it's good now.

Great info. Solved my charging problem! Best video of this type I’ve seen. Thanks!

Apparently I'm that 1%. I used this trick over the winter here in St.Louis and it worked great for heating. Tonight I turned the a/c on and the fan was not coming on. I swapped the wires back and now I have cold air. Looks like I need to run that common wire.

Great Video!!!! Thanks Bud.... What happens if your dealing with an old system that does not have Common connection in it?

Great vid worked for me very Thankful N appreciated

I love how you produced this video. Well made.

Thank you for the video!!! This helped us get our nest up and running again.

Holy crap how many amazing channels does this guy have?!

Thanks so much. This helped me out. Thank god for RU-vid

Great video!!! Thank you very much for taking time to help so many people!!!👍🏼

This is super helpful! I have figured out the problem but not the solution. I have 2 sets of each color going to the furnace. All the colors are correctly positioned from one set. The second set has just the green and white hooked up too! The red and blue wires are cut short and not in use. Anyone know which of the second set should be hooked up and to which outlet? Should they match identical to the first set?

Unbelievable... I've been fighting with no power to my Nest thermostat for 3 days. I thought I was going to have to call a tech and spend $100s of dollars. Weird thing is it worked for 2 years and then, all of a sudden... no power. The wiring at my furnace is like a rat's nest with zones and all. Anyway, I had a green common in both G and C. I never use the fan option so I unplugged the C and switched the G over to C and, bingo! Something was apparently wrong with my C wire. Thank you so much!

Thank you! Thank you! Thank you! (We don't have AC, so I used the yellow as a common wire, but the principle is the same.)

Awesome video. Funny and nice music. I have this problem -- only 4 wires. Going to move the green. Thanks for breaking it down and explaining everything in such detail. Subscribed.

Could I split the G wire between G and C to retain fan control?

Christmas morning and I wake up to a freezing house. After searching for a reason I found this video. My Nest was in stuck in a boot-loop. The Nest was restarting, internal battery low message, shutting down and then restarting again. I called Nest and they said to charge the thermostats internal battery using a USB charger and the USB plug on the thermostat. After an hour of USB charging I plugged the thermostat back into the wall. I had just enough internal battery power to keep the thermostat from restarting while I setup 24v common fix. Voltage has been sitting at 3.906 for the last 24 hours. Thank you for the fix….

Thank you so much. Yes so I wasn’t sure if this applied to me or not. My nest would turn off every couple mins. It would say starting again in 2:45 or something and then it would just be on and off on and off every few mins. So I figured it out. Is your nest power is anywhere around 20mA then you need a common wire. Luckily I noticed a blue wire that wasn’t being used. I opened up the AC unit and it wasn’t connected. I connected it to the C on the mother board then connect to the C on the nest panel. Now I’m putting out 200mA. And my system works great. Also at the same time I found 2 other issues. My nest won’t populate any networks. I found that my WiFi chip is burnt up prolly caused by the on going power issue. If this happens to you. Just contact nest they will be happy to ship you a new display. Also another issue I found was that my AC unit itself was not powering on. After some investigation I found a killswitch on my condensation pan. After draining the water and unclogging the drain line, my AC was back on and kicking. Just some issues I’ve fixed in my house. Hope this helps others.

Great Video and explanation, helped solve my issue with the missing common wire. BUT I disagree with the discussion on the value of independent fan control. Large volumeous homes or homes with separate sources of heating, like fireplaces can benefit from intermittent fan circulation independent to the furnace cycle. Thanks for the help and explanation!

Thank you! Helped me a ton and got my Nest working. You Da MAN!

its about time to switch my heat to cold, but last winter we change to a "modern" furnace and i had enough switching wire C to G so im planning to rewire the system which i found out i dont need to. haha you save my ass thanks for the video

Thank you for sharing your knowledge. Very helpful, indeed. I was ready to take the thermostat back.

Thanks for your video! I don't have an air conditioner/condenser unit. I just have a Furnace... The house was built in 2002... Would this video still apply to me? Thanks again!

Thank you so much! This was such a great explanation!

Great Video...worked for me. Thank you very much!!!

You are a life saver . Thanks man.

Great Video, just solved my issue. Thanks guys.

I have an old "Breaburn" thermostat [with a C wire] in place already. I LOVE my Nest thermostat and I've owned it for over 4 years ~ and I've lived in a few apartments and condo's in Phoenix during those 4 years. But now I'm faced with a "C Wire" scenario / it's here!!. Are you saying I 'don't need the C wire' at all, and the Red wire will be sufficient for power to the Nest? Should I just "disconnect the [C Wire] and stuff it behind the wall / thermostat? Or just simply tell me "which terminal" on the Nest thermostat that I need to plug the [C Wire] into. (if at all)

You're the best. Awesome video. Stoked to follow!