There can be many reasons why your HVAC system is short-cycling. It could be a faulty thermostat, loose wiring, or issues with the HVAC equipment itself.
The Nest thermostat has a “low-temperature differential” which means it is quite sensitive to small temperature changes, triggering the HVAC system to turn on and off more frequently. While this isn't true short-cycling, it has the same impact, by over-working the equipment.
In this article, I dive into what causes short cycling and 9 ways to fix it in your system.
Most Common Reasons for Short Cycling
Although there can be many reasons why short cycling occurs in your system, it mainly revolves around the three basic components of your HVAC system:
- Faults within the thermostat
- Wiring Issues
- Defective HVAC equipment.
When considering the thermostat, it might be glitching out or running into a setting that’s constantly toggling the system on and off.
On top of that, it could be facing power issues due to loose wiring or a lack of a C-wire.
So starting the troubleshooting process at the thermostat itself helps us rule it out quickly and get to the root of the problem faster without having to call the professionals just yet.
Normal Cycle Rate
Typically an air conditioner, or even a furnace, should cycle around 20 minutes every hour.
As such, it should stay on for a maximum duration of 20 minutes and power down for the remainder of the hour.
However, if it's switching on and off nonstop within short intervals (such as every 5-10) minutes, and the temperatures in your home don't seem to be improving, it could indicate short cycling.
First-Time Installers: Check System Compatibility
If the thermostat has just been installed, it's a good idea to confirm that your Nest thermostat is indeed compatible with your existing HVAC system.
Usually, Nest thermostats are compatible with most low-voltage (24V systems), but there can be some exceptions.
So if you're setting up the Nest thermostat for the first time, make sure to check compatibility.
Diagnosing the Issue: Check the Energy History
In the Energy history settings, you can easily identify previous patterns of short cycling and figure out if they were actually a short cycling issue or another problem with the temperature regulation in your home.
In some instances, particularly when a system is oversized and there's not enough insulation in your home, the Nest thermostat's low-temperature differential will show signs of short-cycling.
Whatever the case, checking your energy history can help you get down to the root of the problem efficiently.
How to Check Energy History via Google Home
For the Nest thermostat 2020 model
- Open the Google Home app
- Select your home and thermostat
- From the thermostat’s home screen, head over to “Settings” at the top right (represented by a gear cog icon)
- Then, scroll down to “Energy Dashboard”
- Select, the day, week, or month you want to check the energy history
Check Energy History Via the Nest App
For Nest Thermostat E and Learning Thermostats
- Open the Nest app and select your thermostat
- Then, tap on “History” for a brief 10-day summary of the energy history
- Select any day to get a more detailed graph outlining the energy patterns specific to that day
Access the Energy History Menu Via the Thermostat
Applies to the Nest thermostat E and Learning Models
- For the Nest Learning Thermostat: Wake up the display, then select “History”
- For the Nest thermostat E: Head over to “Settings” and then select the option for “History”
With the energy history settings, you can see if the system improved the temperatures and figure out if it was an actual short cycling error or simply the thermostat’s temperature differential getting in the way.
Troubleshooting Step 1: Manually Adjust the Thermostat
If you think that the issue is due to the low-temperature difference on your Nest thermostat and not an actual short cycling issue, you can carry out a diagnostic test by yourself to see if the HVAC equipment is working correctly.
To carry this out:
- If you're using the cooling equipment, simply increase the temperature by ten degrees from your current indoor temperature and see if the cooling equipment stays powered down
- If you're on heating, lower the temperature by ten or so degrees and see if the heating equipment stays off
- If any of these devices turn on and off, especially when they don't have to, it can indicate a short cycling issue.
- However, if the devices stay off until the desired temperature is reached, and work to maintain that temperature, it won't be a short cycling issue.
This is a decent indicator that helps eliminate the HVAC system and the wiring as being defective. However, to get a better idea, we need to troubleshoot further.
If you suspect that the device is not short cycling and instead, it's due to temperature fluctuations, consider these alternatives:
- Your system might be oversized: Reach out to an HVAC company and get them to size up your equipment accordingly.
- The insulation in your home might not be enough: Don't forget to close any windows and doors. Also, check if there are any openings where heat/cold could be leaking out.
- Thermostat installed in the wrong location: Your thermostat might be in direct sunlight, or in any room that doesn't measure the actual temperature of your home. In that case, relocating the thermostat might be a good idea
- The thermostat's temperature differential is too low: Sadly for Nest thermostats, this isn't adjustable.
Short cycling, regardless of whether it improves the temperatures or not, is detrimental to your HVAC equipment.
Therefore, it's important you try to resolve this issue and extend your heating and cooling cycles to prevent further damage to your equipment.
Step 2. Check Power Information
After you've identified the power-cycling pattern, it's now time to troubleshoot for any power issues on your Nest thermostat.
But before you go replacing the batteries or fiddling around with the wiring, it's easier to head over to the power information menu on the thermostat and make sure everything is running properly in the power department.
You can check these via the mobile apps, but I recommend going through the thermostat just in case you’re running into Wi-Fi issues.
How to Access the Power Information Through the Google Home App
This applies to any model, including the latest 2020 Nest thermostat
- Open the Google Home App and select your thermostat
- After that, head over to settings at the top right
- Scroll to “Device Information” and select the “Power” option.
Access the Power Info Via the Nest App
Applies to the Nest Thermostat E and Learning Models
- Open the app and select your thermostat
- Then, head over to “Settings” → “Technical Info”
- Select the option for “Power.”
On the Thermostat
Only for the Nest Thermostat E and Learning Models
- Wake up the ring and head over to “Settings”
- Then, scroll to “Technical Info” and enter that menu
- After that, navigate to “Power”
What To Look For in the Power Information
Ideally, your battery voltage should be higher than 3.6V and the input current must be higher than 20mA.
If your battery voltage is sufficient, you can skip the next step of recharging or replacing the batteries.
However, if your input current (Iin) is lower than the expected minimum of 20mA, there might be wiring issues in the thermostat.
To learn more about what these values are and how to make sure these are proper, check out this article.
Step 3: Replace or Recharge the Batteries
To make sure you resolve any lingering power issues, the first thing you should do is replace or recharge the batteries on your Nest thermostat.
This helps resolve any power issues and gives the thermostat constant power to signal the HVAC equipment without any interruptions or delays, which is essential to troubleshoot short cycling.
- For the latest Nest thermostat (2020 model), make sure you replace the old batteries with a fresh set of Alkaline AAAs.
- For the Nest Thermostat E and Learning Models, recharge via the Micro or Mini-USB port found at the back of the thermostat display.
Step 4: Restart the Thermostat
Restarting the Nest Thermostat can resolve any software glitches and hopefully, fix your short cycling issue.
To restart the thermostat:
- First access the quick view.
- Then, move to “Settings” then navigate to “Reset.”
- From there, choose “Restart.”
- Provide confirmation to follow through with the restart.
- Then, wait until the device reboots.
- Finally, adjust the temperatures manually and see if the short cycling issue resolves itself.
In case this in-menu option isn't working, you can manually restart it by:
- Pressing down on the ring button for approximately 10 seconds.
- Release, then briefly press the ring button again.
- The thermostat’s screen should go blank and then light up – a clear sign it’s in restart mode.
- After the restart, switch the system mode to ‘Heat' or ‘Cool’
- Then, adjust the temperature and monitor the performance of the HVAC system.
- If the short cycling issue persists, it's time for the next step.
Step 5: Disable Nest Sense Features
If a restart didn't solve the issue, you can try disabling the Nest Airwave and Sunblock features. This can help fix any short cycling or temperature mismatch errors.
However, please note that these features are only available for the Nest thermostat E and Nest Learning thermostats.
Disable Nest Airwave and Sunblock
- Start by clicking the ring on your thermostat, which pops open the Quick-View menu.
- From there, navigate to “Settings”, Nest Sense, and select, “Airwave”
- Here, select the option to turn it off.
- Then, return to the Nest Sense menu and select “Sunblock”
- Turn it off the same way
- Finally, return to the main menu
- Then, wait a couple of minutes and try adjusting the temperature.
- See if the short cycling issue goes away.
You can also disable these features via the Nest app. The instructions are similar once you open the app and select the thermostat.
Long overdue firmware updates can lead to your Nest Thermostat short cycling, as glitches pile up or power handling grows inefficient.
So for good measure, make sure to keep the device updated regularly with a constant connection to the internet.
How to update the firmware varies slightly based on the model of your Nest Thermostat.
But, before you do, make sure the thermostat is connected to the Internet via Wi-Fi.
Update Firmware Via the Nest Thermostat
- For the 2020 Nest thermostat: Navigate from the home screen to ‘Settings,’ then select ‘Version Update'.
- For the E and Learning models: Choose ‘Settings', and then proceed to ‘Software Update'.
In the steps that follow, we talk about how to troubleshoot the thermostat wiring. Touching live wires is risky and has the potential to cause serious injury or electrical fires.
So if you're uncertain or inexperienced, we recommend getting help from a professional.
Step 6: Check the Thermostat Wiring
Although issues with loose wiring are not as common with the Nest thermostat, troubleshooting the wiring is still a crucial step.
The wiring contacts on the thermostat, especially for the heating or cooling equipment might be loose, creating intermittent connections and resulting in a system that appears to be short cycling.
So if you’re up to the task, I highly recommend checking the thermostat wiring.
At SmartHomePerfected we always advise readers not to undertake any work they are not competent in performing and if in any doubt, it is best to seek the assistance of a professional.
Diagnose the Physical Wiring Behind the Thermostat
- First, pull the thermostat off the display and see if any of the wires are loose or disconnected.
- If you notice any issues or want to rewire the connections and make sure they are solid, start by turning off the power to the thermostat.
- After that, press down on the connector and tug on each wire to remove them from the thermostat terminal.
- Make sure the wires are clean with enough copper exposed to create a decent electrical connection. (They should be stripped to about 1/3″ to 1/2″.)
- After cleaning and stripping the wires, make sure to install them in the proper terminals. Don’t forget that the connector tabs should be held down, ensuring a tighter connection.
- Take a photo of the wiring setup or note down the installed wires.
- Finally, replace the thermostat display and restore power to the thermostat.
Confirm the Wiring In the Thermostat’s Settings
After you plug in the thermostat and it reboots or restores the connection with the HVAC equipment, you must confirm the wires are detected in the equipment menu on the thermostat display. Here’s how:
- Open the settings and navigate to “Technical Info” → “Equipment.”
- For the Nest thermostat 2020 model: this setting might be “Device Information” → “Equipment”
- After you enter the equipment menu, you'll be shown the thermostat wiring connections and the detected wires.
- Verify all the wires are detected by cross-referencing them with the photo you took.
- If the wires are detected, they should be indicated in the wiring diagram. If not, they will be grayed out.
If the wires match the actual photo, you can try adjusting the temperature and checking if the short-cycle issue is resolved.
Otherwise, you might have to troubleshoot the wires further or reconfigure the equipment.
Checking the Thermostat Cable
To troubleshoot the wires and the entire length of the thermostat cable, you might have to check the terminals on the other end of the thermostat cable (which is the furnace or HVAC system’s control board) and also make sure the wiring isn't damaged in between.
This is best done with the help of a professional.
To reconfigure your equipment, you might have to reset the Nest thermostat or select “Continue” on the wiring diagram and follow the instructions.
This setting will show you which system modes are set up in your device along with the option to customize any settings related to the HVAC system and thermostat wiring.
Check the C-Wire
If you don't have a C-wire hooked up to your thermostat already, now might be a good time to consider one.
Almost half of the power issues I've seen in the Nest thermostat can be easily resolved by installing a C-wire for better power stability.
If you don't have an extra wire to install, don't worry, there are several alternatives to installing a new wire or thermostat cable.
For solutions related to the C-wire, check out this article.
Step 7: Bypass the Thermostat
As I mentioned in the intro, bypassing the thermostat or jumping the thermostat wires is the best way to figure out if the thermostat or HVAC equipment is at fault here.
However, this method is not recommended for anybody who isn't skilled in electrical DIY. So if you’re not comfortable handling the thermostat wires, I recommend skipping this step and getting help from a professional.
Still here? Then here’s how you can jump the thermostat:
- First turn off the power to the thermostat and HVAC system
- Then, pull the thermostat off the wall mount
- Take out the R wire along with the Y and W (Cooling and heating)
- Then, jump the R wire with the Y or W as necessary. You can do this with wire nuts or by twisting the copper contacts together.
- Then, restore power and see if the heating (if you jumpered R and W) or cooling (for R and Y) turns on.
- Give it a good couple of minutes to see if you notice any short cycling.
- If it doesn’t short cycle, repeat steps 2-5, but this time with the other wire (Y or W)
If you notice the heating or cooling equipment short cycling, you can be certain that the issue lies within the HVAC system and not the thermostat.
The Thermostat is Faulty
However if the HVAC equipment turns on and stays on without cutting in and out, it’s definitely the thermostat that’s causing the issue.
In that case, a factory reset is your final solution before you deem the thermostat as defective and get help from a professional.
Usually, you might need to replace the device. So if you have an old thermostat laying around, you can try installing it and see if the short cycling problem goes away.
Step 8: Reset the Thermostat
If you've followed all the previous instructions, including the bypass procedure, your only option to redeem the thermostat is to carry out a factory reset.
However, please note that a factory reset deletes all your custom settings and schedules. So note down any settings before you follow through with this final resort.
For direct steps on carrying out a full factory reset, including how to delete the thermostat from the mobile apps, check out this article.
Step 9: Check the HVAC Equipment
If you're confident that it's not the thermostat, you can turn your attention to the HVAC system.
- Dirty/Incompatible filters
- Low or leaking refrigerant issues
- Weak Airflow
- Faulty control boards
- Loose contactors or relays
Can aggravate the short cycling issue, so it’s best to resolve these as soon as possible.
Call in the Professionals
For troubleshooting a faulty thermostat and troublesome HVAC equipment, I recommend getting help from a professional.
They’ll be able to get to the root of the issue faster and repair or replace any components that need fixing.