Expanded manufacturer code library
Google Nest expanded error-code library
Every Google Nest error code on this site, grouped by product: thermostat, Protect alarm. Choose the exact product family first, then read the code exactly as your display shows it, because the same characters can have unrelated meanings on a different device.
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32 complete records in this directoryGoogle Nest Protect alarm showing a green ring: alarm over: meaning and exact next steps
a green ring: alarm over means Conditions are returning to normal. Google says the smoke or carbon monoxide level is decreasing.
Open record Google Nest Protect alarm · exact showingGoogle Nest Protect alarm showing a pulsing green ring at night: meaning and exact next steps
a pulsing green ring at night means Normal. Google says Protect constantly monitors its sensors, batteries and Wi-Fi, and each night when the lights are off it glows green to show everything is working.
Open record Google Nest Protect alarm · exact showingGoogle Nest Protect alarm showing a red ring: Emergency: meaning and exact next steps
a red ring: Emergency means Emergency. Google says smoke or carbon monoxide has reached emergency levels in the room named.
Open record Google Nest Protect alarm · exact showingGoogle Nest Protect alarm showing a yellow ring and a chirp every 60 seconds: meaning and exact next steps
a yellow ring and a chirp every 60 seconds means The batteries are very low. Google says only a few days of battery life remain and Protect starts chirping day and night soon. A single chirp every 60 seconds continues until you replace the batteries.
Open record Google Nest Protect alarm · exact showingGoogle Nest Protect alarm showing a yellow ring and two chirps every 60 seconds: meaning and exact next steps
a yellow ring and two chirps every 60 seconds means Protect has expired under safety regulations. Google says Protect sounds a double chirp once a minute, and that you will not be protected from smoke or carbon monoxide if you do not replace it.
Open record Google Nest Protect alarm · exact showingGoogle Nest Protect alarm showing a yellow ring, chirp every 60 seconds (CO sensor): meaning and exact next steps
a yellow ring, chirp every 60 seconds (CO sensor) means Carbon monoxide sensor failure. Google says Protect tested its CO sensor and detected a problem.
Open record Google Nest Protect alarm · exact showingGoogle Nest Protect alarm showing a yellow ring, chirp every 60 seconds (smoke sensor): meaning and exact next steps
a yellow ring, chirp every 60 seconds (smoke sensor) means Smoke sensor failure. Google says Protect tested its smoke sensor and detected a problem.
Open record Google Nest Protect alarm · exact showingGoogle Nest Protect alarm showing a yellow ring: batteries low: meaning and exact next steps
a yellow ring: batteries low means The battery is low. Google says Protect (or the backup batteries in a wired Protect) needs new batteries in the coming months.
Open record Google Nest Protect alarm · exact showingGoogle Nest Protect alarm showing a yellow ring: Heads-Up: meaning and exact next steps
a yellow ring: Heads-Up means Heads-Up early warning. Google says Protect detected rising smoke or carbon monoxide levels and the alarm may sound.
Open record Google Nest Protect alarm · exact showingGoogle Nest Protect alarm showing a yellow ring: offline: meaning and exact next steps
a yellow ring: offline means Protect is no longer connected to the internet. Google's message on the phone is that Protect is offline.
Open record Google Nest Protect alarm · exact showingGoogle Nest Protect alarm showing no lights and a chirp every 60 seconds: meaning and exact next steps
no lights and a chirp every 60 seconds means Light ring failure. Google says the Protect's light ring no longer works and the message is that the sensors have failed.
Open record Google Nest Protect alarm · exact showingGoogle Nest Protect alarm showing no power light (power out): meaning and exact next steps
no power light (power out) means Power out. Google says a wired Nest Protect's wired power is out and it is running from its battery.
Open record Google Nest thermostat · exact codeGoogle Nest thermostat code E10, E30, E66, E80, E116, E160, E196, E296, M13: meaning and exact next steps
E10, E30, E66, E80, E116, E160, E196, E296, M13 means The thermostat detects no power to the Y1 wire, which Google labels a cold-weather shutoff. Nest thermostats can use the Y1 (air conditioner) wire to keep charged when there is no common wire, and an air conditioner's low-pressure safety switch can stop sending that power in very cold weather. Google also says the cause can simply be a system that needs maintenance.
Open record Google Nest thermostat · exact codeGoogle Nest thermostat code E109, E110, E111, E112, E113 and E439 to E443: meaning and exact next steps
E109, E110, E111, E112, E113 and E439 to E443 means The thermostat detects a conflict involving the G (fan) wires. Google words them as: G2 detected and G1 also required (E109, E439); G2 detected, remove the W2/AUX wire (E110, E440); G2 detected, remove the E wire (E111); G or G3 detected and G1 and G2 also required (E112, E442); G2 and O/B conflict (E113, E443).
Open record Google Nest thermostat · exact codeGoogle Nest thermostat code E12, E32, E82, E162: meaning and exact next steps
E12, E32, E82, E162 means The thermostat detects no power to the W1 (heating) wire.
Open record Google Nest thermostat · exact codeGoogle Nest thermostat code E14, E34, E84, E164, E264, E414: meaning and exact next steps
E14, E34, E84, E164, E264, E414 means A dual-fuel system (a heat pump with a backup furnace) needs an alternate heat wire, and the thermostat does not find one.
Open record Google Nest thermostat · exact codeGoogle Nest thermostat code E157, E158, E194: meaning and exact next steps
E157, E158, E194 means The thermostat does not detect an expected wire. Google words E157 as Y1 wire not detected, E158 as W1 wire not detected and E194 as R wire not detected.
Open record Google Nest thermostat · exact codeGoogle Nest thermostat code E2, E22, E72, E402: meaning and exact next steps
E2, E22, E72, E402 means The thermostat detects no power wires. Google says an Rc or Rh wire is required.
Open record Google Nest thermostat · exact codeGoogle Nest thermostat code E257, E258, E294: meaning and exact next steps
E257, E258, E294 means The wires were not configured properly in the Google Home app. Google words them as: heat pump requires Y1 wire (E257), W2 wire requires W1 (E258) and R wire is required (E294).
Open record Google Nest thermostat · exact codeGoogle Nest thermostat code E3, E23, E73, E195: meaning and exact next steps
E3, E23, E73, E195 means The thermostat detects no power to the Rc wire. Google's table words E195 as no power to the R wire.
Open record Google Nest thermostat · exact codeGoogle Nest thermostat code E450, E451, E452: meaning and exact next steps
E450, E451, E452 means A wiring conflict on the Nest Learning Thermostat (4th generation): E450 is an AQ and star wire conflict, E451 says dual transformers require the Y3 wire on AQ+, and E452 says Y3 requires Y2.
Open record Google Nest thermostat · exact codeGoogle Nest thermostat code E52, E102, E182 and the other overcurrent codes: meaning and exact next steps
E52, E102, E182 and the other overcurrent codes means The thermostat detected an overcurrent on one of its wires. Google says its internal breaker has tripped 10 or more times, which means a recurring problem that will not go away by itself. Which wire to check depends on the code: E52, E102 and E182 are W1; E53, E103 and E183 are Y1; E54, E104 and E184 are G; E55 and E105 are O/B; E56 and E106 are W2/Aux; E57 and E107 are Y2; E58, E108 and E188 are the star or star/O-B terminal.
Open record Google Nest thermostat · exact codeGoogle Nest thermostat code E8, E28, E78, E408: meaning and exact next steps
E8, E28, E78, E408 means Additional wires are required because a W2/AUX wire was detected by itself.
Open record Google Nest thermostat · exact codeGoogle Nest thermostat code H1, H2, H71, H72 and the other H codes: meaning and exact next steps
H1, H2, H71, H72 and the other H codes means A Heat Link problem on a system with a domestic hot water tank, OpenTherm, a condensing boiler, district heating or Fil pilote. H1, H71 and H151 mean the thermostat cannot connect to the Heat Link (its light is yellow); H2, H72 and H152 mean the thermostat lost power; H73 and H153 mean it cannot detect the system's OpenTherm; H155 means the Heat Link went offline when its batteries were low; H156 means OpenTherm wiring was set up without selecting OpenTherm; H157 and H158 mean the Heat Link was removed from the app or account.
Open record Google Nest thermostat · exact codeGoogle Nest thermostat code M13, M20, M22, M23, M26 and the other M codes: meaning and exact next steps
M13, M20, M22, M23, M26 and the other M codes means M codes are a mix of informational messages and problems, and Google's table points each to its own article: M13 is the cold-weather no-power code, M20 is a "No power" alert, M22 means the thermostat is offline, M23 means a thermostat wire is undetected or unconfigured, M26 means it cannot connect to a Matter device, M12 means a Nest Temperature Sensor is not in a good spot, M19 is about changing thermostat batteries and M21 means it is unable to update software.
Open record Google Nest thermostat · exact codeGoogle Nest thermostat code N1, N21, N71, N401 and the other low-power N codes: meaning and exact next steps
N1, N21, N71, N401 and the other low-power N codes means One wire is receiving power, but less than expected. Google names the wire for each code: N1, N21, N71 and N401 mean the Rc power wire is not connected to equipment; N2, N22, N72 and N402 mean the same for Rh; N3, N23, N73, N153 and N403 are W1; N4, N24, N74, N154 and N404 are Y1; N5, N25, N75 and N405 are W2/AUX; N6, N26, N76, N156 and N406 are G; N7, N27, N77 and N407 are O/B; N28, N78 and N408 are Y2; N29, N79, N159 and N409 are the star wire; N414 is no power to AQ+ on a one-wire accessory and N415 is an AQ- wire without an AQ+ wire.
Open record Google Nest thermostat · exact codeGoogle Nest thermostat code N262, N263, N412, N413: meaning and exact next steps
N262, N263, N412, N413 means In extremely cold weather only: no power to the Y1 wire is detected, the same cold-weather shutoff as the E10 group. N412 also appears on Google's list for a system that needs maintenance.
Open record Google Nest thermostat · exact codeGoogle Nest thermostat code N416, N417, N418, N419, N420, N421, N422, N423: meaning and exact next steps
N416, N417, N418, N419, N420, N421, N422, N423 means The thermostat detected an overvoltage or overcurrent error on the HVAC equipment. Google says the HVAC system may need maintenance.
Open record Google Nest thermostat · exact codeGoogle Nest thermostat code T01, T02, T03 and the other T codes: meaning and exact next steps
T01, T02, T03 and the other T codes means A system-test problem: the test after installation found that one part of the system did not respond. Google's list: T01 single-stage fan, T02 single-stage cooling, T03 two-stage cooling, T04 forced-air system, T05 radiant heating, T06 radiator heating, T07 baseboard electric heating, T08 humidifier, T09 dehumidifier, T11 two-stage fan, T12 three-stage fan.
Open record Google Nest thermostat · exact codeGoogle Nest thermostat code TD001, TD003, TH003 and the other TD and TH codes: meaning and exact next steps
TD001, TD003, TH003 and the other TD and TH codes means The thermostat has trouble connecting: TD001, TD005 to TD008, TD010 to TD012, TD014 to TD017 and TD019 to TD022 mean it is having problems connecting to Wi-Fi or the app (Google's article is for a thermostat that is offline); TD003, TD004, TD009, TD018, TD023, TD024, TD027, TD028 and TD030 occur while adding the thermostat to the app; TH codes (TH003, TH004, TH008 to TH011, TH013 to TH019 and TH026) cover Wi-Fi and Thread network setup problems.
Open record Google Nest thermostat · exact codeGoogle Nest thermostat code W3, W4: meaning and exact next steps
W3, W4 means The thermostat failed to connect. For W3, Google says the router is not giving the thermostat a network IP address. For W4, the thermostat is connected to the wireless network but not to the internet.
Open record Google Nest thermostat · exact codeGoogle Nest thermostat code W5: meaning and exact next steps
W5 means The thermostat cannot connect to Wi-Fi. Google says this can indicate a hardware malfunction, and the thermostat may need replacing.
Open recordGoogle Nest codes, lights and chirps
Google Nest devices report problems in three ways: help codes on a thermostat's screen, colored light rings on a Protect alarm and spoken or chirped messages. A thermostat code such as E8, E28, E78 or E408 usually means a wiring or power issue, for example an auxiliary heat wire connected without the wires it normally pairs with. A Protect with a yellow ring is asking for attention: a yellow ring with a message about batteries means they are low and need replacing within months, and two chirps every minute with a yellow ring signals an expired alarm.
Press the Nest button on a Protect to hear what it is reporting, and open the Google Home app to see the matching notice. Turn off the power before touching thermostat wiring, take a photo of the base wiring first, and compare it with the wiring diagram from setup. Smoke and carbon monoxide alarms are safety devices, so replace expired units rather than silencing them. Each code, ring color and chirp pattern has its own page with the maker's meaning.
Nest products signal faults in different ways, so the first job is to identify the device. A Nest thermostat shows help codes and messages in the Google Home app, and a Protect shows colored rings, spoken warnings and chirp patterns. A thermostat that says it needs extra wires is reading the wiring in its base, and the answer is in the wiring diagram you made at setup. A Protect that chirps every minute needs its batteries or has expired.
Smoke and carbon monoxide alarms are life-safety devices, so replace expired or faulty ones, and test them monthly. Turn off the power at the breaker before touching thermostat wires, and use a professional if you are unsure.
What does a yellow ring on a Nest Protect mean?
It is a heads-up that something needs attention, such as low batteries, and the spoken message tells you which.
Is it safe to change Nest thermostat wires myself?
Switch off the power at the breaker, photograph the wiring and follow the diagram. If you are unsure, use an HVAC technician.
How often should I test a Nest Protect?
Test it monthly by pressing the Nest button, and replace the alarm when it reaches the end of its life.