Direct answer
For the Nest Learning Thermostat (4th gen), microphone/wake, account linking, device name/room and provider service should be separated. First, test a basic local assistant command and inspect mute status.
What this covers
- Nest Learning Thermostat (4th gen) (GA05551)
- Google Nest/Home device; Matter/Thread role, wired/battery power, subscription and Google Home migration vary.
- The specific fault this record addresses: does not respond to voice control
What it does not cover
- ×The same symptom on a different Google Nest product line, which has its own record and its own cited source
- ×An on-screen error code whose meaning has not been checked against this exact model's manual
- ×Live electrical, gas, sealed-system, internal battery-cell or structural repair — a technician boundary, not a self-service step
Differential
What actually causes this, and how to tell them apart
These are ordered by how often each one is the answer, not by how easy it is to try. The point of the middle column is that two causes producing the same headline symptom rarely produce the same detail — that detail is what tells you which one you have before you change anything.
- 1
The device name does not match what is being said
What separates it Other commands work and one device never responds. Assistants match on the name and room recorded in the linked account, which can differ from what the manufacturer's app shows.
How to confirm Ask the assistant to list the devices it knows about, and use exactly the name it reports. A name with a number, a duplicate, or a room prefix is a common mismatch.
- 2
The account link has expired or was never completed
What separates it Voice control stopped on a date, or has never worked, while the manufacturer's own app is fine. Links expire on password changes and on some platform migrations.
How to confirm Unlink and relink the account rather than re-adding the device. The device is not the broken part.
- 3
Two devices share a name or a room
What separates it The wrong device responds, or nothing does because the assistant cannot disambiguate. Duplicate names are created easily and are invisible until a command is ambiguous.
How to confirm List the devices the assistant knows and look for repeats. Renaming one is the whole fix.
- 4
The requesting person is not a recognised member
What separates it One household member is refused and another is not. Voice profiles and household membership gate personal results and some device control.
How to confirm Compare the same command spoken by the owner and by the member.
- 5
The action itself is not exposed to voice
What separates it The device responds to some commands and reports that it cannot do others. Not every capability is exposed through every assistant, and security actions in particular are commonly restricted or require a spoken code.
How to confirm Check the assistant's documented capability for that device type rather than assuming parity with the manufacturer's app.
- 6
The thermostat is restricted from voice adjustment
What separates it Temperature queries are answered and changes are refused. Several platforms restrict setpoint changes by voice, particularly where a schedule or a lock is active.
How to confirm Try reading the temperature and setting it as two separate tests. One working and the other not is a restriction rather than a fault.
Before you touch a setting
Record this first — changing settings destroys the evidence
Every item below stops existing the moment a reset, re-pair or settings change is made. Written down first, they are what separates the causes above; recovered afterwards, they are guesswork.
- The exact words spoken, verbatim. Paraphrasing a failing command loses the thing that made it fail.
- Exactly what the assistant said back, if anything — a refusal, a wrong device, silence and a misheard word are four different failures.
- The device's name as the assistant reports it, not as the manufacturer's app shows it.
- Whether the same command works for another household member.
- Whether other commands to the same device work, which separates the link from the phrasing.
Control the device in its own app
ReversibleWorking there and failing by voice puts the fault in the assistant link, not in the device. This is worth establishing before touching any voice setting, because the two are commonly confused.
Ask the assistant to list the devices it knows
ReversibleUse exactly the name it reports back. Assistants match on the name and room held in the linked account, which can differ from what the manufacturer's app displays — and a mismatch there is silent.
Look for duplicate names and duplicate rooms
ReversibleTwo devices sharing a name means the assistant either picks the wrong one or refuses to pick at all. This is invisible until a command is ambiguous, and renaming one device is the entire fix.
Repeat the command as another household member
ReversibleVoice profiles and household membership gate personal results and some device control. One person refused and another accepted is a membership question rather than a device one.
Separate reading a value from changing it
ReversibleSeveral platforms answer queries and refuse changes, particularly for thermostats, locks and alarms. One working and the other not is a documented restriction, not a fault to chase.
Relink the account rather than re-adding the device
Signs you outLinks expire on password changes and platform migrations, and the device itself is not the broken part. Unlinking and relinking preserves the device's own settings, where removing and re-adding it discards them.
Model-specific
What is true of this model and not of its siblings
Generic advice for the product line fails here. Each item below is a property of this specific model family that changes which of the steps above apply to you.
- Model scope
- GA05551. Google Nest/Home device; Matter/Thread role, wired/battery power, subscription and Google Home migration vary.
- Display
- A 2.7-inch (68 mm) diameter circular liquid crystal display at 600 x 600 pixels. Round and high resolution — not the 2.4-inch 240 x 320 rectangular panel in the cheaper Nest Thermostat, which is the quickest way to tell which model you actually have.
- Sensors
- A Soli sensor for Motion Sense, plus temperature, humidity and ambient light. Soli is radar rather than a passive infrared detector, so its presence behaviour differs from the plain motion sensor in the Nest Thermostat.
- Power
- Powered from HVAC system wiring with a built-in rechargeable lithium battery. This is a sealed rechargeable cell — not the 2 AAA alkaline batteries used by the Nest Thermostat. 'Replace the batteries' is not a step on this model, so a low-power symptom here is a wiring or charging investigation.
- Consumption
- Less than 1 kWh per month.
- C wire
- Patented Power Sharing technology; Google states it is designed to work whether or not the home has a common (C) wire, and that in limited cases — fewer than 1% — a C wire or a Nest Power Connector may be necessary to guarantee sufficient power in all conditions.
- Wi-Fi
- 802.11n on 2.4 GHz and 5 GHz. Dual-band.
- HVAC stages
- Works with most 24V systems — gas, electric, oil, forced air, heat pump and radiant. It controls heating in 1, 2 and 3 stages (W1, W2, W3); cooling in 1, 2 and 3 stages (Y1, Y2, Y3); heat pump up to 3 stages with 1 or 2 stages of auxiliary/alternate and emergency heat (O/B, AUX, AUX2, E); fan (G, G2, G3); power (C, RH, RC); humidifier and dehumidifier (HUM, DEHUM); and ventilation (VENT). That is far beyond the single-stage-plus-one the Nest Thermostat supports.
- Connector limits
- Google states the * connector can accept only ONE of W3, Y3, G3, E, HUM or DEHUM. The AQ+ and AQ- connectors accept only Y3, or 1-wire or 2-wire VENT, HUM or DEHUM. On a system that needs more than one of those, this constraint decides the installation before anything else does.
- Power path
- Drawn from the HVAC control wiring. A dedicated common wire supplies continuous power; without one, the thermostat charges from the heating circuit and can hold enough charge for the display while failing at sustained radio use.
- Symptom boundary
- This record covers Google Nest Nest Learning Thermostat (4th gen) when it does not respond to voice control. A different symptom on the same hardware, or this symptom on a different Google Nest product line, has its own record with its own causes and its own cited source.
Stop boundary
When this stops being a self-service repair
Continuing past any one of these costs more than the repair saves — in safety, in warranty, or in evidence a technician needs.
- !Account linking fails repeatedly with a provider-side error that neither app can resolve.
- !Voice is being relied on as the only way to operate a lock, alarm or access device — it should never be the sole path.
- !The assistant consistently misidentifies who is speaking in a way that exposes personal results to the wrong person.
Evidence ledger
Sources behind this answer
Visible sources support the visible claims. Home Product Support records the publisher, the fact used and the review date; community reports can suggest an issue but do not become a published fact on their own.
Where the manufacturer's article stops. Google Nest Help publishes this as "Google Nest thermostat help". Official Google Nest thermostat setup, scheduling, HVAC and Wi-Fi help. What that article does not carry is the model boundary — it is written for a product line, and GA05551 is the scope applied here. Where a control label, terminal, indicator pattern or reset sequence differs on your unit, the manual for that exact model is the authority, not this page and not the article.
Exact questions
Common follow-ups
How do I tell the Learning Thermostat from the cheaper Nest Thermostat?+
Look at the screen. The Learning Thermostat (4th gen) has a 2.7-inch circular display at 600 x 600 pixels; the Nest Thermostat has a 2.4-inch rectangular 240 x 320 panel behind a mirrored lens. That is the fastest reliable check, and it matters because the two have genuinely different wiring capabilities.
Can I replace the batteries in the Learning Thermostat?+
No — it uses a built-in rechargeable lithium battery charged from the HVAC wiring, not the 2 AAA alkaline cells used by the Nest Thermostat. So a low-power symptom on this model is a wiring or charging investigation, and swapping batteries is not a step that exists here.
Does it need a C wire?+
Google states it is designed to work with or without one, using its Power Sharing technology, and that in fewer than 1% of cases a C wire or a Nest Power Connector may be needed to guarantee sufficient power in all conditions. So the answer is normally no, with a small and specifically acknowledged exception.
How many heating and cooling stages does it support?+
Up to 3 stages of heating (W1, W2, W3) and 3 of cooling (Y1, Y2, Y3), plus heat pump up to 3 stages with 1 or 2 stages of auxiliary or emergency heat. That is substantially more than the Nest Thermostat, which handles one stage of each plus a second stage of either — the main reason to choose this model on a complex system.
Can it run my humidifier and ventilation at the same time?+
Watch the connector limits. Google states the * connector accepts only ONE of W3, Y3, G3, E, HUM or DEHUM, and the AQ+/AQ- connectors accept only Y3 or 1-wire or 2-wire VENT, HUM or DEHUM. On a system needing several of those, this constraint decides the installation before anything else.
Does it support 5 GHz Wi-Fi?+
Yes — 802.11n on both 2.4 GHz and 5 GHz.
Why does it wake when I walk past and my old one did not?+
It uses a Soli radar sensor for Motion Sense rather than a passive infrared detector. Radar responds differently to approach and to movement behind objects, which is why its presence behaviour does not match the plain motion sensor in the Nest Thermostat.
Other commands work but this one device never responds.+
That exonerates the microphone, the wake word and the service entirely — the problem is the device link or the name. Ask the assistant to list what it knows and use exactly the name it reports back, which is often not what the manufacturer's app displays.
The wrong device responds.+
You almost certainly have two devices sharing a name or a room, which the assistant cannot disambiguate. This stays invisible until a command is ambiguous. Listing the devices the assistant knows finds it, and renaming one is the whole fix.
Voice control worked and then stopped with no changes.+
Account links expire — commonly on a password change or a platform migration. The device is not the broken part, so unlink and relink the account rather than removing and re-adding the device, which would discard its settings for nothing.
It hears me but does the wrong thing.+
That is intent matching, not the microphone — the words were transcribed and matched to a different action. What the assistant said back is the diagnostic here, and the exact phrasing matters, so record the command verbatim rather than paraphrasing it.
It refuses to change the temperature but will tell me what it is.+
Several platforms answer queries and restrict setpoint changes, particularly where a schedule or a lock is active. One working and the other not is a documented restriction rather than something to troubleshoot.
My partner can control it and I cannot.+
Voice profiles and household membership gate both personal results and some device control. Running the identical command as each person is the test, and the answer is a membership setting rather than anything on the device.
Can I use voice to unlock the door?+
Where a platform allows it at all, it normally requires a spoken code, and many restrict it entirely. That restriction is deliberate: a voice command is audible through a door and by anyone in the room. Voice should never be the only way to operate a lock.
Should I re-add the device to fix voice control?+
Not as a first step. Removing and re-adding a device discards its name, room, automations and shares — all to fix a link between two accounts that unlinking and relinking would have repaired without touching the device at all.
Does this answer apply to every Google Nest model?+
No. It is scoped to GA05551. Google Nest/Home device; Matter/Thread role, wired/battery power, subscription and Google Home migration vary.
What should I record before troubleshooting voice control or Alexa or Google?+
Record the complete model identifier, exact message or indicator, software/firmware where visible, the operating stage and what still works.
Why is a factory reset not the first step?+
A reset can erase accounts, networks, maps, schedules or preferences without distinguishing voice control, Alexa, Google. The ordered checks preserve that evidence.
When should I stop and use qualified service?+
Do not disclose voice history or account credentials.
Answer for the exact device and software version shown above.