When the temperature in your home is not as comfortable anymore as it should be, it might be because your Nest thermostat has started to cycle on and off. The question is then whether you can troubleshoot and fix the issue yourself.  

In most cases when your Nest thermostat is turning on and off, you will be able to find the problem and fix the issue yourself.  Issues such as worn-out batteries and worn fuses can easily be rectified by yourself. However, if old wiring has to be replaced or your thermostat is encountering software problems, you’ll most probably have to contact a qualified technician. 

In this article, we provide you with an easy way to conduct your troubleshooting. We’ve determined 6 categories to which the cycling between on and off issues might be related. Usually, you’ll find that only one of the categories is involved. 

We discuss each category and give you tips on how the problem can be fixed. The categories are not given in a specific order, so you can start your troubleshooting with any of them. 

Categories to troubleshoot your Nest thermostat’s cycling issue

The issues causing your thermostat to turn on and off are usually related to one of the following: 

Categories Possible issuesDIY solution?
WiringOld/wrong wiring Loose connectionsMay need professional help Generally DIY
BatteriesReplaceable batteries flat Built-in battery gone bad DIY Replace thermostat
FuseBlown fuse Dirty fuse contact pointsDIY DIY
Placement of thermostatNear other heat sources or in direct sunlightDIY
Software Need updates Bugs DIY May need professional help
Other HVAC devicesFault in one or more devicesMay need professional help
Common reasons and solutions to why nest thermostat keeps turning on and off

Reason 1 – Wiring-related problems

If your Nest thermostat keeps cycling on and off, the problem might be wiring-related.

A) Old incompatible wiring or wrong wiring connections

The problem

If the cycling problem has started soon after you’ve replaced your thermostat or one of the HVAC devices, there is a great possibility that the wiring was accidentally incorrectly done during the replacement procedure, or that the thermostat is not compatible with the existing wiring. The C wire may also be connected to the wrong thermostat terminal. If the connections are incorrectly done, power will not flow to the thermostat’s battery, and when the battery gets drained, the thermostat may start turning on and off.  

The possible solution

To rectify the problem, look again at the wiring diagrams and instructions you’ve received with the thermostat or device and compare the connections with your thermostat and devices. Remember to turn off all the power to your thermostat and HVAC system before you start working on the wiring. 

When you find wires which are incorrectly connected, change them around and re-connect correctly. To check whether you’ve fixed the problem, turn the HVAC system and your thermostat on again. Wait for about two hours to give the battery time to charge and check whether your thermostat is still turning on and off. If not, you’ve solved the problem. 

If the problem persists

If the issue persists, troubleshoot the other categories and if the problem is still not solved after all your troubleshooting, you’ll have to contact your HVAC technician for assistance. The technician will then among other tests, test the compatibility of the new thermostat with your home’s existing wiring. 

B) Loose connections

The problem

Loose connections in your HVAC system may prevent the smooth flow of electric current to the thermostat. This can cause the battery to drain faster than it charges and the thermostat might cycle on and off. Bad connections as such can also trigger the thermostat to cycle.

The possible solution 

To find the loose connections, you can use the “Tech Info Diagram” feature your Nest thermostat offers. Find the option for this feature on your thermostat and open it. The diagram shows all the loose connections in red.

Tech info diagram demo

Turn off your HVAC system’s electricity, remove the thermostat display from the base on the wall, and find the loose connections shown in the diagram. Secure all the wires and where needed, re-insert the wire into the thermostat’s connector. To re-insert a wire properly, press down the connector button and push the wire as far as it will go. The wire has been properly installed if the connector button remains in its position when you let it go. 

When you’re satisfied that all the connections, including the thermostat’s connections, are securely in place and correctly aligned, fit the display back to the base and power on the system.

If the cycling stops in about two hours, you’ve been successful! 

If the problem persists

However, if the on and off cycling persists you have to keep on troubleshooting.

Reason 2 – Battery-related problems

Battery-related problems are often the reason why your thermostat is turning on and off.

A) Flat replaceable batteries

The problem

Some Nest thermostats are equipped with 2 AAA batteries to supplement power if the HVAC system’s power is insufficient. These batteries also act as a backup option in the event of a power outage. When they’ve become old and don’t have a high power charge anymore, it may cause the thermostat to cycle on and off.  

The solution

Replace the 2 batteries with identical new ones and the problem might be solved.

To replace the batteries, you have to switch off all electrical power to the thermostat and then plug out the Nest thermostat from the wall. Remove the old batteries from their socket and replace them with 2 new 1.5V AAA alkaline batteries.

Return the Nest thermostat to its position on the wall and turn the power on again. If the batteries have been the problem the thermostat will now not cycle anymore.

Replace Nest thermostat battery

If the problem persists

If the problem persists, you have to troubleshoot the other categories. 

B) Built-in battery

The problem

Many Nest thermostats are equipped with a rechargeable built-in battery. When it has worn out after a few years, it can’t hold sufficient power anymore. It drains fast and shuts down the thermostat. But as worn-out batteries also charge just as fast as they drain, the result is that the thermostat keeps turning off and on as the battery is drained and charged. 

The solution

The only way to fix this problem is to replace the thermostat. 

Reason 3 – Fuse-related problems

As the HVAC system’s current is relayed via the HVAC fuse a faulty fuse influences the whole system

A) Blown fuse

The problem

A blown fuse causes no power to go to the thermostat and its built-in battery. And as explained earlier in this article, a drained battery causes the thermostat to cycle on and off. If you don’t fix a blown fuse the built-in battery will in time totally drain and the thermostat will completely shut down.

The solution

Locate the system’s fuse. Usually, it is connected to the control unit within your HVAC. Turn off the power to your HVAC system and remove the fuse. When you’ve removed the fuse, look at the u-shaped wire visible through the fuse’s transparent “window.” The fuse is blown if the u-shaped wire is broken.

If the fuse is blown, replace it. Just remember, when you replace the fuse, you have to replace it with the same model as the one that has blown. The color of a fuse is also important as it indicates the current rating. 

After you’ve replaced the blown fuse, turn on the system again and if the thermostat is after about two hours not cycling anymore, the issue has been resolved.

Blown fuse repair

Important note

When you’ve replaced the blown fuse and it blows again when you put the system on again, it is recommended that you contact a licensed technician to rule out and fix any issues. 

B) Dirty fuse contact points

The problem

Even when the fuse is not blown, a dirty or loose fuse can also cause intermittent power losses that can cause the thermostat to keep on cycling.

The solution

If the fuse is not blown, clean the contact points on the fuse and inside the fuse holder and put the fuse back. As a fuse is not an expensive component, it might be a good idea to replace the fuse in any case. 

After you’ve put the fuse back again turn on the system again and check after about two hours whether the cycling has stopped.

Reason 4 – Placement-related problems

A) Near other heat sources or in direct sunlight

The problem

A heat source like a table light, stove, kettle, toaster or TV screen, or direct sunlight may cause the thermostat to frequently turn on and off. The heat from a source in your home, or direct sunlight can convey an inaccurate temperature to the thermostat. This high-temperature reading can create the impression that it is overheating.  The wrong impression of overheating forces the thermostat to shut down as it tries to protect its components. When the heat source is turned off or the direct sunlight is blocked the thermostat clicks on again. You experience this as a thermostat turning on and off the whole time. 

The solution

These inaccurate overheating readings can easily be rectified. Just relocate the thermostat to a place where it is not near a direct heat source or in direct sunlight. 

Reason 5 – Software-related problems

A) Need updates

The problem

Like all smart devices, your Nest thermostat also needs software updates from time to time. When the thermostat starts to act strange, including cycling on and off, it might be because the latest software version has not been installed. 

The solution

A manual update might solve the cycling problem and keep the thermostat running smoothly. It is easy to update your thermostat. Just follow these steps:

  • Press the Nest ring on the thermostat.
  • Navigate to settings.
  • Click on the software tab.
  • Click the update tab.
  • Wait for the update to complete.

After you’ve updated the software, ensure that the system and thermostat are powered on and check after about two hours whether the thermostat has stopped cycling on and off. If it has stopped, check the thermostat at least once a day for a few days to make sure that the problem is not returning.

Nest Thermostat manual update demo

B) Software bugs

The problem

Even excellent thermostats like the Nest thermostats can develop software and bug issues. Different bugs have different effects on the thermostat. A software bug can, for instance, cause the Nest thermostat to cycle on and off. Other bugs might affect the charging of the battery and make it drain faster than it should. The thermostat will then start cycling on and off. These bugs often occur after a faulty or incomplete software update.

The solution

A software update often clears the software from bugs. If you detect that there are still active bugs after your latest update has been done, it is better to contact a Nest professional.

Reason 6 – Other HVAC device-related problems

If your troubleshooting actions regarding wiring, battery, fuse, thermostat and software have not been successful, the problem may be a fault with one or more HVAC devices. 

A defective HVAC device may cause some strange behavior from your Nest thermostat, such as frequently turning on and off. This usually happens because the device is prohibiting the Nest thermostat from drawing enough power from the HVAC system.

To find the faulty device in the HVAC system and fix it, you’ll, unfortunately, need to call an HVAC technician to run tests on the system. Depending on the results of the tests the technician will be able to either fix the problem or replace the faulty device. 


Even well-designed and sophisticated thermostats like the Nest thermostats can develop issues that cause them to cycle on and off. Fortunately, you can do the troubleshooting to a great extent by yourself. In most instances, you will also be able to fix the issues yourself and don’t have to call a qualified technician every time. 

Just remember to power off the HVAC system, including the thermostat, before you start with the troubleshooting and fixing process. 


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