Nest Thermostat Error E4: Why Is There No Power to W1 and How Do I Fix It?
- W1 wire disconnected
- Loose connection at furnace
- Blown fuse on furnace board
Problem Description
Nest error E4 indicates the W1 heating wire is not receiving power or is disconnected. Your heating system cannot activate because the signal wire to the furnace is not working.
Symptoms
- Nest shows E4 error
- Heat not turning on
- W1 wire no power message
- Furnace not responding to heat calls
- Cool works but heat does not
- Thermostat shows heating but nothing happens
Recognize these? Here's what usually causes it.
Common Causes
- W1 wire disconnected
- Loose connection at furnace
- Blown fuse on furnace board
- W1 wire damaged
- Furnace control board issue
- Wrong terminal connection
Most fixes happen in the first 3 steps.
Do not bypass E4 error by jumping wires. Improper wiring can damage furnace or create safety hazards.
Tools & Requirements
These tools will help you complete this fix.
Multimeter
Klein Tools 80196 Digital Multimeter Kit with Case, ...
Screwdriver
STREBITO 155 in 1 Electric Screwdriver Set, Small El...
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Step-by-Step Solution
Check W1 at Nest Base
Turn off HVAC power. Remove Nest from base. Verify white W1 wire is firmly inserted in the W1 terminal. Wire should be stripped 1/2 inch and pushed fully in.
Check W1 at Furnace
At furnace control board, locate W terminal. Verify white wire from thermostat connects securely to W. A loose connection here causes E4.
Check Furnace Fuse
Locate 3-5 amp fuse on furnace control board. If blown, replace with same amperage. Blown fuse can interrupt W1 circuit.
Test Wire Continuity
Disconnect W1 at both ends. Use multimeter continuity mode to test wire from Nest to furnace. No continuity means damaged wire that needs replacement.
Needed for this step
Klein Tools 80196 Digital Multimeter Kit with C...
$46.15Verify Correct Terminal
Some systems have W1 and W2. Ensure single-stage heating uses W1. Two-stage systems need both. Check your HVAC manual for correct wiring.
Quick Solutions
Still having issues? This is usually the deeper cause below.
If drain continues after replacing batteries, check the event history — a stuck-open sensor or rapid polling loop burns through batteries in days.
If you have a heat pump, the heating wire might be connected differently. Check your system type in Nest settings.
Thermostat issues that keep returning are often caused by stale backup-battery memory holding old settings across power cycles without the user realising.
- W1 wire disconnected
- Loose connection at furnace
- Blown fuse on furnace board
- W1 wire damaged
- Furnace control board issue
Before you go — try one of these (they fix most cases).
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Official Manufacturer Manual
Google Nest provides official product documentation through their online manual rather than downloadable PDF. Access setup guides, troubleshooting steps, and product specifications for your Google Nest Thermostat.
Source: google.com
Need More Help? Google Nest Support
Note: The contact information below connects you directly to Google Nest's official customer support team, not Trunetto. They can help with warranty claims, device replacements, and advanced technical issues.
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