Nest Thermostat Not Turning On Furnace? (Quick Fix Guide)

Is your Nest thermostat not turning on furnace? This is a well-known and easy-to-fix issue!

Whenever a Nest thermostat is not turning on the furnace, this ultimately means that the device will not start heating until further notice.

The furnace problem may be related to many different possibilities, and in this guide, we’re going to unwrap everything and help you fix your problem!

If your Nest thermostat is not turning on the furnace, verify that the safety temperature is disabled and that the device is receiving power. You must check whether the orientation settings are configured correctly.

Let’s continue to unwrap!

Why is the Nest Thermostat Furnace Not Turning On?

Your Nest thermostat may be unable to turn on the HVAC furnace due to many different aspects involving everything from the power to the settings.

So, the very first step before getting into the troubleshooting would be to reveal all potential causes to familiarize yourself with them quickly.

Here’s everything that may prevent your Nest thermostat’s furnace from working:

Even if those possibilities appear frightening, we’ve managed to produce a helpful guide that will tackle each of them in no time.

So, no technical skill is required, only a few minutes of your time!

How to Fix When Nest Thermostat Not Turning on Furnace?

Tip: Follow the steps chronologically!

1. Disable Your Nest *Safety* Settings

If you didn’t know, Nest thermostats have safety settings designed to protect your home from freezing or overheating.

This feature will automatically turn on the heat or the cooling when a certain temperature threshold has been reached, which sometimes interferes with the furnace.

So, the solution would be to disable the safety settings (temporarily) and test whether the heat and furnace will start working.

The method of disabling is different for the base Nest thermostat and the Nest Learning/E, so follow the respective steps as per your equipment.

Disable Safety Settings (Nest Thermostat):

1. First, verify that your Nest thermostat is working.
2. Go to the Settings and tap “Safety Temperature.”
3. Use the slider to select a lower or a higher temp.

Disable Safety Settings (Nest Learning/E):

1. First, open the Google Home app on your device.
2. Then, touch the tiles and navigate to “Settings.”
3. From there, change your “Safety Temperature.”

When you’ve tweaked the settings, check whether the furnace will turn on when necessary, and if the problem continues, keep reading further into the guide…

2. Replace the Nest Thermostat Battery

When the furnace of your Nest thermostat is not turned on, one of the most important factors to consider is the power supply to the thermostat.

The Nest thermostat is operated by replaceable batteries, except for the Nest thermostat E or Nest Learning. 

So, if you’ve got the base model of the Nest thermostat, you must replace the batteries to justify whether the issue comes from the charge.

The Nest thermostat uses a set of 1.5 V AAA alkaline batteries, so make sure only to use high-quality units.

Nest E & Nest Learning: Charge via USB Cable!

The battery cannot be replaced if you have the Nest E or Nest Learning thermostat, so you must manually charge the thermostat.

This is only possible using a USB cable, which you can hook up to any adapter or your computer’s USB ports, which will trigger a blinking light on the device.

Note: Leave your thermostat charging for an hour, then test the furnace!

3. Tweak the Nest Orientation Settings!

Many Nest thermostat users with a heat pump in their Nest system most commonly experience furnace-related issues with the thermostat.

This primarily happens due to incorrect O/B settings, which are responsible for changing the direction of the refrigerant in the heat pump and valve.

This is the primary functionality that enables the thermostat to cool when needed and heat when necessary.

When there is a fault with these settings, the Nest thermostat furnace may not work.

Change O/B Settings on Nest Thermostat:

1. Open the Google Home or Home app.
2. Then, you must select a Nest thermostat.
3. Tap on the “Settings” section from the top.
4. Select your Nest thermostat from the tab.
5. Scroll down to locate the “Heat Pump” tile.
6. If the “O” option is highlighted, select “B.”
7. If the “B” option is highlighted, select “O.”
8. Test whether the furnace is now working.

Change O/B Settings on Nest Learning/E:

1. On the thermostat, navigate to the “Settings.”
2. Then, select “Equipment” and tap “Continue.”
3. Next, choose “Heat Pump” to get redirected.
4. If the “B” option is selected, change it to “O.”
5. If the “O” option is selected, change it to“B.”
6. Test whether your furnace is now turning on.

If you still continue to experience the same furnace-related problem, you may need to perform a power cycle on your thermostat and test again.

If this doesn’t help either, restart the HVAC from the primary circuit, test again, and continue with the next solution.

4. Check the Thermostat Furnace Wiring

If you have identified that only the HVAC furnace is not turning on when necessary, the issue may be related to the thermostat’s wiring.

The furnace wiring comprises 6 wires connecting to the G, W1, RH, and C, “*” and “W2AUX” connectors. 

This applies to all Nest thermostats, and the number of wires you must inspect depends on the model and functionalities of your thermostat.

Here’s how all furnace wires must be connected:

Warning: Turn OFF the power to your thermostat and HVAC from the primary circuit!

• The green wire connects to the “G” terminal.
• The white wire goes to the “W1” terminal.
• The blue wire connects to the “C” terminal.
• The red wire connects to the “RH” terminal.
• The brown wire goes to the “W2AUX” terminal.
• The black wire goes into the “Star” terminal.

When you remove your Nest thermostat from the wall, you’ll see all the wires exposed and whether they are disconnected.

So, follow the aforementioned tips of connecting all the wires and ensure they are not damaged.

Tip: We recommend unplugging and reconnecting the wires into their respective terminals!

5. Update the Nest Thermostat System

Sometimes, the problem with the communication comes from an outdated thermostat system, and to restore functionality, you must perform an update.

Luckily, it’s effortless to update the thermostat, but your device must be connected to the internet to download the system firmware.

Here’s how to update your Nest thermostat in easy steps:

1. First, verify that your thermostat is working.
2. Then, from the Quick View, go to “Settings.”
3. Then, enter the “Software Update” section.
4. If a new firmware is found, select “Update.”

When the update starts, you must remain patient until the system updates, and when ready, you may test whether the thermostat will turn on the furnace.

If you continue to experience the same issue, jump to the final step from the guide…

6. Factory Reset Your Nest Thermostat!

If your Nest thermostat not turning furnace on, the final and most potent solution would be to perform a factory reset.

This method will entirely reset all the settings and configurations on your thermostat and revert the system to default, which might help erase all the system bugs!

Here’s how to factory reset your Nest thermostat in easy steps:

1. On the Nest thermostat, go to the Settings.
2. Then, locate and select the “Reset” option.
3. From the list, you must select “All Settings.”
4. To begin the process, tap the “Reset” option.
5. You must scroll the ring to confirm the reset.

The factory reset on your Nest thermostat lasts 2-3 minutes, so remain patient until your unit reboots, and you’re sent to the “Equipment Detected” screen.

Then, press “Continue” to set up your thermostat, and when ready, the furnace fault should be gone, and the heating will work.

Tip: For more help, contact Google Nest Help.

Quick Recap:

Hence, when the Nest thermostat not turning on furnace, disable the safety temperature settings and correct the O/B feature setup.

In addition, you must verify that all the wiring is correct, replace the thermostat’s battery, and perform a factory restoration to default!

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