Nest Thermostat Error E104: What Is This Critical Error and How Do I Fix It?
- Short circuit in wiring
- Wire touching wrong terminal
- Damaged wire insulation
Problem Description
Nest error E104 is a critical overcurrent error indicating too much electrical current is flowing through the thermostat wiring. This is a safety hazard that can damage the thermostat or HVAC equipment.
Symptoms
- Nest displays E104 error
- Critical overcurrent message
- Thermostat shut down
- Fire hazard warning
- System unresponsive
- E104 after electrical work
Recognize these? Here's what usually causes it.
Common Causes
- Short circuit in wiring
- Wire touching wrong terminal
- Damaged wire insulation
- HVAC equipment malfunction
- Transformer voltage too high
- Multiple systems overloading
Most fixes happen in the first 3 steps.
If E104 appeared after DIY electrical work, double-check all connections. A single wire in the wrong place can cause overcurrent.
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
Turn Off Power Immediately
E104 indicates potential fire hazard. Go to your circuit breaker and turn off power to HVAC system immediately. Do not attempt to use the system until issue is resolved.
Inspect All Wiring
With power OFF, remove Nest from backplate. Carefully inspect every wire. Look for bare copper touching other wires or metal. Check for melted or burnt insulation.
Check for Short Circuits
A short circuit causes overcurrent. Look where wires enter the wall - they may be pinched or damaged. Check at the furnace end too for any wires touching where they should not.
Test Transformer Voltage
Using a multimeter, test the HVAC transformer output. Should be 24-28 VAC. If significantly higher, the transformer may be failing and sending too much power to Nest.
Needed for this step
Klein Tools 80196 Digital Multimeter Kit with C...
$46.15Call HVAC Professional
E104 is serious. If you cannot find obvious wiring issue, call a licensed HVAC technician. They have tools to diagnose overcurrent sources safely. Do not ignore this error.
Quick Solutions
Still having issues? This is usually the deeper cause below.
Schedules that skip randomly are usually a daylight-saving holdover — delete and recreate the schedule to clear the corrupted entry.
E104 is one of the most serious Nest errors. It protects against electrical damage and fire. Never try to bypass or ignore it.
Thermostat issues that keep returning are often caused by stale backup-battery memory holding old settings across power cycles without the user realising.
- Short circuit in wiring
- Wire touching wrong terminal
- Damaged wire insulation
- HVAC equipment malfunction
- Transformer voltage too high
Before you go — try one of these (they fix most cases).
Most popular upgrades chosen by Google Nest Thermostat owners.
Google Nest Thermostat Trim Kit - Made for the Nest Therm...
Google Nest Thermostat Trim Kit - Made for the Nest Therm...
Google Nest Thermostat - Smart Thermostat for Home - Prog...
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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.
How Does Google Nest Compare?
Before replacing your Google Nest device, see how it stacks up against alternatives in our full comparison guides.
