Nest Thermostat Not Working?
Fix blank screens, "Delayed" messages, low battery warnings, and error codes on all Google Nest models. Most issues are caused by a missing C wire.
Last updated: February 2026
Safety Warning
Always turn off the HVAC breaker before removing your Nest from its base or touching any wires. While the thermostat wires are low-voltage (24V), the furnace connections carry dangerous 120V/240V.
Common Nest Problems & Quick Fixes
Black/blank screen
Charge via USB for 30+ min. If recurring, install C wire.
"Delayed" message
C wire missing. Use Nest Power Connector ($25) or install C wire.
Blinking green light
Restarting/updating. Wait 15 min. If stuck, USB charge needed.
"No power to Rh/Rc wire"
Check breaker. Inspect R wire connection. Check furnace fuse.
Won't connect to Wi-Fi
Must be 2.4GHz. Re-enter password. Check signal strength.
Temperature reading wrong
Sunlight or draft on sensor. Go to Settings > Temperature to check.
8-Step Nest Troubleshooting Guide
Check the display and battery level
Press the Nest ring to wake it up. If the screen is completely black, the battery is dead. Pull the thermostat off the base and charge it via USB (micro-USB for 2nd/3rd gen Nest Learning, USB-C for 2020 Nest Thermostat) for at least 30 minutes. While charging, go to step 2 to check your electrical system. If the screen turns on, go to Settings > Technical Info > Power — the battery should read 3.7V or higher.
Check the circuit breaker and HVAC power
Find the HVAC breaker in your electrical panel and ensure it's in the ON position. Also check for a power switch on or near your furnace — it looks like a light switch and is sometimes accidentally turned off. If the breaker keeps tripping, you may have a short circuit in the HVAC system — this needs professional attention.
Check for error codes and messages
If your Nest screen is on, look for error messages. Common ones: "No power to Rh wire" — the heating circuit has no power (check wiring). "No power to Rc wire" — the cooling circuit has no power. "Delayed" — the Nest doesn't have enough power to activate HVAC (C wire issue). "E73" — the C wire is missing or not connected. "W5" — heating ran for too long (safety shutoff). Note the exact code for troubleshooting.
Verify your Nest wiring
Turn off the HVAC breaker. Pull the Nest display off the base. Take a photo of the wiring. Verify each wire is fully pushed into the correct connector — you should see the metal wire inside the clear connector window. Gently tug each wire to confirm it's secure. The most important connections: R or Rh (red, power), W (white, heat), Y (yellow, cool), G (green, fan), and C (blue, common). If there's no C wire, this is likely the root cause of battery and power issues.
Run the equipment test
Go to Settings > Equipment > Continue > Test. The Nest will test each HVAC component one at a time (heating, cooling, fan). Listen for the system to start when each test begins. If a test fails (you hear nothing or get an error), the issue is with that specific system. If all tests pass but the system doesn't work normally, the issue is with scheduling, Home/Away, or temperature settings.
Restart your Nest thermostat
Press and hold the Nest ring for 10 seconds until the screen turns black. Release and wait — it will restart within 60 seconds. This clears temporary software glitches. If the Nest is frozen or unresponsive to touch, pull it off the base, wait 10 seconds, and push it back on. This forces a power cycle.
Check Wi-Fi and software updates
Go to Settings > Network and verify you're connected to your Wi-Fi network with at least 2 bars of signal. If offline, select your network and re-enter the password. Then go to Settings > Software > Update to check for pending updates. Outdated firmware can cause erratic behavior. Ensure your Google Home app is also up to date on your phone.
Factory reset as last resort
If nothing else works, go to Settings > Reset > All Settings. This erases your schedule, Wi-Fi settings, and preferences — the Nest will behave as if freshly installed. After reset, go through the setup process again. If problems persist after a factory reset, the thermostat hardware is likely faulty and needs replacement (check your Nest warranty — it's 2 years from purchase).
If these steps resolved your issue, your thermostat should now be working correctly.
Pro Tip
Check your Nest's battery voltage at Settings > Technical Info > Power > Battery. Healthy = 3.7-3.9V. Below 3.6V = power problem. Below 3.5V = won't function reliably. If it keeps dropping, you need a C wire — not more USB charging.
The C Wire Problem (Root Cause of 70% of Nest Issues)
The single most common cause of Nest thermostat problems is a missing C (common) wire. The C wire provides continuous 24V power. Without it, the Nest tries to trickle-charge through HVAC cycles — and this often isn't enough, causing:
- Random blank screens and restarts
- "Delayed" messages when trying to start heating or cooling
- Low battery warnings despite charging via USB
- Wi-Fi disconnects (the Nest shuts off Wi-Fi to conserve power)
- HVAC short-cycling (turning on/off rapidly)
Three ways to fix the C wire problem:
Install a Nest Power Connector ($25)
EasyEasiest option. Installs at your furnace. No new wiring needed. Converts an existing wire to provide C wire power.
Run a new C wire
HardMost reliable solution. Run a new thermostat wire from furnace to thermostat. Best done during renovations or by an electrician.
Use an add-a-wire kit ($20-30)
MediumUses the existing thermostat cable to add C wire functionality. Works if you have at least 4 existing wires.
Related Nest Guides
Frequently Asked Questions
Written by
ThermostatFixer Editorial Team
Our team of HVAC enthusiasts and DIY experts creates detailed thermostat troubleshooting guides, wiring diagrams, and repair tips to help homeowners fix common thermostat issues without calling a technician.