Direct answer
For the Nest Learning Thermostat (4th gen), trigger, conditions, controller/hub, permissions and action chain should be tested separately. First, review activity history and trigger the action manually.
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: routine, schedule or automation is not running
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 trigger never fired
What separates it Nothing appears in the activity history at the expected time. Running the action manually works perfectly, which is what convinces people the automation is broken when the action is the one part that is fine.
How to confirm Check the history first. No entry means the trigger, not the action — and every minute spent on the action is wasted.
- 2
A condition was false at the moment it fired
What separates it The history shows the automation evaluated and did nothing. Conditions on presence, time of day, sunset, another device's state or a household member's location fail silently by design.
How to confirm Remove conditions one at a time and re-run. A routine that works with no conditions and fails with one identifies that condition exactly.
- 3
Time zone or location is wrong on the home, not the phone
What separates it Everything runs, at the wrong time — often by a whole number of hours, or with sunrise and sunset offset. The home's location is a separate setting from the phone's, and it defaults to wherever it was created.
How to confirm Check the home or hub's own time zone and address rather than the phone's. Sunset-based automations firing at a consistently wrong hour is this and almost nothing else.
- 4
Presence detection is the trigger and it is unreliable
What separates it Arriving and leaving automations fire late, early, twice, or not at all — and worse for one household member than another. Geofencing depends on the phone's location permission, its background activity allowance and its power state.
How to confirm Compare each member's phone permissions. A geofence needs 'always' location rather than 'while using', and battery optimisation defeats it silently.
- 5
One action failed and stopped the chain
What separates it The first part of a routine happens and the rest does not, consistently at the same point. Actions run in order and a failure partway leaves a half-executed result.
How to confirm Run each action individually. The one that fails alone is the one that is stopping the chain, and it usually has its own separate fault.
- 6
The automation belongs to an account that lost access
What separates it It stopped on a date that matches someone leaving the home, a password change or a device being re-added. Automations are owned, and ownership is not always transferred when a device changes hands within the household.
How to confirm Check which account created the routine and whether that account still has permission to the devices it touches.
- 7
Two automations are fighting
What separates it The result flickers, or the last state does not persist. A schedule and a sensor rule that disagree will each keep applying their own outcome.
How to confirm Look for another routine touching the same device at an overlapping time. This is invisible from either routine's own screen.
- 8
The device was renamed or moved to another room
What separates it The automation exists and references something that no longer resolves. Renaming a device or moving it between rooms breaks rules that referenced it by name or by room.
How to confirm Open the routine and confirm each referenced device still resolves rather than showing a placeholder.
- 9
The thermostat's own schedule is overriding the automation
What separates it The temperature reverts shortly after the automation sets it. A learned or programmed schedule and an external automation are two controllers issuing conflicting instructions.
How to confirm Check whether a schedule or a learning feature is active. Suspending it for one test separates the two cleanly.
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.
- Whether the automation appears in the activity history at all at the expected time — this single check splits trigger problems from action problems.
- The exact time it should have run and the exact time anything happened, because an offset of whole hours is a time-zone answer.
- The full list of conditions attached to it, before any are removed.
- Which account created the routine, and whether that account still has access to every device it touches.
- Whether it fails always, or only overnight, or only when nobody is home — each points somewhere different.
- For presence triggers, each household member's location permission and background activity allowance.
- Any other routine or schedule that touches the same device at an overlapping time.
Read the activity history before changing anything
ReversibleAn entry at the expected time means the trigger fired and the problem is downstream. No entry means the trigger never fired and nothing about the actions is worth investigating. This one look decides which half of the work is real.
Run every action manually, one at a time
ReversibleActions execute in order and a failure partway leaves a half-run routine. Running each alone identifies which one stops the chain, and that action almost always has its own separate fault worth fixing on its own terms.
Check the home's time zone and location, not the phone's
ReversibleThe home has its own location setting and it defaults to wherever it was created. Everything running at a consistently wrong hour, or sunrise and sunset landing wrong, is this and very little else.
Remove conditions one at a time and re-run
ReversibleConditions fail silently by design — presence, time window, sunset offset, another device's state. A routine that works with none and fails with one has told you exactly which condition is false at the moment it matters.
Verify presence permissions on every phone involved
ReversibleA geofence needs 'always' location rather than 'while using', and background activity has to be allowed. Battery optimisation defeats both silently, and the symptom differs per household member because the settings do.
Look for a second routine touching the same device
ReversibleTwo rules that disagree each keep applying their own result, which shows as flicker or as a state that will not persist. This is invisible from either routine's own screen and has to be looked for deliberately.
Check whether the device's own schedule is overriding you
ReversibleA learned or programmed thermostat schedule and an external automation are two controllers issuing conflicting instructions. Suspend the schedule for one test rather than fighting it with more automation.
Confirm every referenced device still resolves
ReversibleRenaming a device or moving it between rooms breaks rules that referenced it by name or room. The routine still exists and still appears valid; it simply points at nothing.
Run it twice at the intended time and state
ReversibleOnce proves it can work. Twice, at the real trigger time and in the real household state, proves it does. Automations that pass a manual test and fail in life are failing on a condition that manual testing never reproduces.
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 routine, schedule or automation is not running. 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.
- !The automation is relied on for anything safety-critical — heating for a vulnerable person, medication reminders, access for someone who cannot let themselves in. Consumer routines are best-effort and are not specified for that.
- !The controlling account is inaccessible and the routines cannot be edited or reassigned.
- !The thermostat's behaviour suggests the equipment rather than the schedule — short cycling, failure to reach setpoint, or a call for heat that the system does not answer.
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 "Learn to fix strange heating or cooling issues". Google's own article for a thermostat/HVAC system behaving unexpectedly (stays on, won't turn on, cycles repeatedly) — the closest match to a schedule/automation not running as expected; US/Canada systems only, per the article's own note. Verified reachable and content-matched via the Browser tool 2026-08-28. 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.
The action works when I run it by hand but the routine never fires.+
That is the clearest possible evidence the action is fine and the trigger is not. Check the activity history — no entry at the expected time means nothing downstream is worth investigating, and running the action manually only confirms the part that already worked.
Everything runs an hour off.+
Check the home's own time zone and address rather than the phone's. The home has a separate location setting that defaults to wherever it was created, and an offset of a whole number of hours — or sunrise and sunset landing wrong — is almost always this.
My arrival routine fires late, or twice, or not at all.+
Geofencing depends on the phone, not the home. It needs 'always' location permission rather than 'while using', and background activity has to be allowed — battery optimisation defeats it silently. That is also why it behaves differently for different household members: their phone settings differ.
Half the routine runs and the rest does not.+
Actions execute in order, and one failing stops the chain. Run each action on its own to find which one fails alone — it will usually have a fault of its own worth fixing independently, and the routine will then complete.
The temperature keeps reverting after my automation sets it.+
You have two controllers disagreeing. The thermostat's own schedule or learning feature is re-applying its setpoint over yours. Suspend that schedule for one test rather than adding more automation to fight it.
It stopped working and nothing changed.+
Something usually did. Check for a device renamed or moved to a different room, a household member who left, a password change, or a device removed and re-added. Routines reference devices by name and room, and reference the account that owns them.
The light flickers between two states.+
Two automations are fighting over the same device — commonly a schedule and a sensor rule that disagree. Neither routine's own screen shows the other, so it has to be looked for deliberately by checking everything that touches that device in the same window.
Should I delete and rebuild the automation?+
Not before reading the history. A rebuild that happens to work teaches you nothing about which of the four parts failed, and the same cause will take out the next routine you build. Diagnose first, rebuild only if the routine is genuinely corrupt.
Can I rely on this for something important?+
No consumer automation platform is specified for safety-critical use. Trigger, condition, controller and action each fail independently and silently, and none of them alerts you when they do. Anything that matters needs a layer that is designed to fail loudly.
Why did it work when I tested it and not in real life?+
Because a manual test skips the conditions. Presence, time window, sunset offset and another device's state are all true when you are standing there testing and frequently false at the real trigger moment. Test at the intended time, in the intended household state, twice.
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 routine or automation?+
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 routine, automation. The ordered checks preserve that evidence.
When should I stop and use qualified service?+
Do not use consumer routines as the sole safety-critical control.
Answer for the exact device and software version shown above.