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Nest thermostat troubleshooting: model, reset, entry key and Matter linking

Updated October 28, 2026 · Steps paraphrased from each platform's or maker's own help pages, linked beside each step. We have not tested these steps ourselves.

Short answer

How do I fix or reset my Nest thermostat?

Start by finding which of Google’s 6 Nest thermostat models you have: Google says to look at the display, the base or the Nest app, because the menus differ by model. Then restart it from Settings (a restart keeps your settings) before you reset it, and write down the wiring first (Settings, Equipment): a factory reset erases your settings and you set the thermostat up again in the app.(Google: which Nest; Google Nest: reset)

Offline after you changed your router or Wi-Fi password? Google’s first fix is to give the new network the same name (SSID) and password as the old one. Matter linking error (help code M26)? The usual causes are a low battery, no Wi-Fi, a thermostat not yet added to Google Home, or the limit of 5 linked Matter apps.(Google: offline thermostat; Google: help codes)

As of October 28, 2026, our catalog lists 2 Google Nest thermostat records with a CSA Matter certificate for the exact model and a verified US store link; the models are in the table at the end.(our catalog)

As of . Steps are paraphrased from the platforms’ and makers’ own help pages, linked on the guide; we have not tested them ourselves. Sources: Google: which Nest; Google Nest: reset; Google: offline thermostat; Google: help codes.

Which Nest thermostat do I have?

Google’s identification page covers six: the Nest Thermostat, the Nest Thermostat E, and the Nest Learning Thermostat 4th, 3rd, 2nd and 1st generation. The display, the base and the Nest app each show the model; the Nest Thermostat has a mirrored screen and a touch bar on the right side of the ring, and the Thermostat E a translucent white screen.(Google: which Nest)

Why it matters: the 4th generation Learning Thermostat and the Nest Thermostat are set up in the Google Home app, while the 3rd generation and Thermostat E use the Nest app; their menus, entry keys and reset paths differ.(Google: can’t connect)

See also: Which Nest thermostats work with Matter · Best Matter smart thermostats

Where is the entry key, QR code or setup code?

You must be at the thermostat: Google says you touch it to add it to your account, so it cannot be added remotely. If the thermostat has been used before, factory reset it before you continue.(Google: get started (4th gen))

  1. Nest Thermostat and Nest Learning Thermostat (4th gen): in the Google Home app tap Add Device and scan the thermostat’s QR code. If it will not scan, tap Use setup code and type the code for your device.(Google: get started (4th gen))
  2. 4th gen, to see the fallback entry key: press the thermostat display to bypass the QR code and reveal the alphanumeric key, then enter it in the Google Home app.(Google: can’t connect)
  3. Nest Learning Thermostat (3rd gen or earlier) and Thermostat E: press the ring for Quick View, turn to Settings and press, choose Nest app, then Get Entry Key. The thermostat shows a 7-character key.(Google: can’t connect)
  4. In the Nest app tap Settings, Add product, Continue without scanning, pick your thermostat model and type the 7-character key. If the key does not generate, clear your old account connections and make sure you are on 2.4 GHz Wi-Fi.(Google: can’t connect)

See also: Where is the Matter setup code?

Restart or reset a Nest thermostat

A restart keeps all your settings and helps when the thermostat is frozen, cannot connect or misbehaves. A reset erases some or all of its information and returns it to factory defaults, which is useful if you move or leave the thermostat behind. Write down the wire setup first (Settings, Equipment) and save the other settings.(Google Nest: reset)

  1. Nest Thermostat and Nest Learning Thermostat (4th gen): go to Settings, then Restart or Factory Reset, and confirm. After a factory reset you set it up and add it to your home in the app again. To unlink it from your account, go to Settings, Account, Disconnect.(Google Nest: reset)
  2. Nest Thermostat E and Nest Learning Thermostat (3rd gen or earlier): go to Settings, then Reset, and choose Restart, or reset the schedule, Home/Away, the account connection, the network, or all settings. Remove the thermostat from your account in the app before you reset all settings.(Google Nest: reset)
  3. Frozen and the menu does not work? Manual restart. Nest Thermostat: take it off its base, remove both AAA batteries, put them back and press it onto the base until it clicks. Thermostat E or Learning Thermostat: press the thermostat down for about 10 seconds until the screen turns off, then press and release the ring.(Google Nest: reset)

My Nest thermostat is offline

When it is offline you cannot control it from the app, but you can still set the temperature on the thermostat itself.(Google: offline thermostat)

  1. Changed your router or network? Make sure the new one uses the same network name (SSID) and password as the old one.(Google: offline thermostat)
  2. Connected to Wi-Fi but offline in the Google Home app? Check your phone has a working connection, restart your Wi-Fi router and the thermostat, and update the Google Home app.(Google: offline thermostat)
  3. Check the battery. A low battery stops the thermostat using Wi-Fi to save power; a dark yellow light on the front means it is low, and Settings, Equipment, Power info shows the status on the 4th generation.(Google: offline thermostat)
  4. Still offline: reset the network settings from the thermostat’s Reset menu and reconnect it to your Wi-Fi, check strict firewall or parental-control settings on the router, and as a last resort remove it from the app and reset it. That erases saved schedules and settings.(Google: offline thermostat; Google: can’t connect)

See also: Matter device not responding or offline · Matter Wi-Fi requirements (2.4 GHz, IPv6)

Matter linking errors (help code M26)

The Nest Learning Thermostat (4th gen) and the Nest Thermostat are set up in Google Home first; Matter linking to another app comes after. Google says IPv6 must be on for your home network before you add Matter devices, or control eventually fails even if setup seems to work.(Google: help codes; Google: prepare for Matter)

Google’s M26 list: low battery (replace it with two high-quality 1.5 V AAA alkaline batteries); Wi-Fi unavailable; the thermostat was never added to the Google Home app; it is already linked to the maximum of 5 Matter apps (remove one you no longer use); or it shows “Matter linking is currently unavailable”. For that message, wait and retry, then restart the thermostat and check Settings, Network, Nest server says connected; failing that, factory reset it and add it back to Google Home.(Google: help codes)

See also: Add a Matter device to Apple Home · Use one Matter device with two apps · Which Nest thermostats work with Matter

Nest thermostat records we list

These are the Google Nest thermostat records in our catalog with a CSA certificate for the exact model and a US store link, as of October 28, 2026. The thermostat guide covers the other Matter thermostats.(our catalog)

ProductNetworkWhere the reset steps are
Nest Learning Thermostat (4th gen)Wi-FiReset: see the model sections above(Google Nest: reset)
Nest Thermostat (2020)Wi-FiReset: see the model sections above(Google Nest: reset)

Guides: Best Matter smart thermostats · Which Nest thermostats work with Matter

When to stop and contact Google

Google’s thermostat pages send you to its thermostat troubleshooter first, and then to the Google Home and Nest Community or to Google support. Contact Google when a restart, a reset and the router checks above have not brought the thermostat back, or when it shows a help code that the help-codes page does not fix. Have the model from the identification step ready.(Google Nest: reset; Google: help codes)

Frequently asked questions

How do I find the entry key on a Nest Learning Thermostat 4th generation?

Press the thermostat display to bypass the QR code and reveal the fallback entry key, then type it into the Google Home app, per Google’s help page.

How do I factory reset a Nest thermostat?

On the Nest Thermostat and the 4th generation Learning Thermostat go to Settings, then Restart or Factory Reset. On the Thermostat E and older Learning Thermostats go to Settings, then Reset. Write down the wire setup first.

Why is my Nest thermostat offline after I changed routers?

Google says the new router needs the same network name (SSID) and password as the old one; then restart the router and the thermostat.

How many Matter apps can a Nest thermostat connect to?

Google’s help-codes page says a maximum of 5 Matter supported apps; remove one you no longer use to add another.

Sources

The steps above are written in our own words from these pages. Menus and wording in the apps can change; when they differ, follow the app and the page linked here.