Why Won't My Nest Thermostat Turn On Auxiliary or Emergency Heat?
- Nest Heat Pump Balance set to Max Savings blocking aux
- Auxiliary heat lockout temperature set too low
- O/B wire configured incorrectly for heat pump system
Problem Description
Your Nest thermostat is not activating auxiliary heat or emergency heat when the heat pump cannot keep up with demand. The house stays cold and never reaches the set temperature even though the heat pump is running. The Nest may be trying to be energy efficient by avoiding auxiliary heat but in cold weather this leaves your home uncomfortably cold. This is one of the most common Nest complaints from heat pump owners.
Symptoms
- House never reaches set temperature in cold weather
- Heat pump runs continuously but house stays cold
- Nest shows heating but auxiliary heat never activates
- Temperature drops below set point and stays there
- Aux Heat label never appears on Nest display
- Emergency Heat option not available in Nest settings
Recognize these? Here's what usually causes it.
Common Causes
- Nest Heat Pump Balance set to Max Savings blocking aux
- Auxiliary heat lockout temperature set too low
- O/B wire configured incorrectly for heat pump system
- Nest not detecting aux heat wire connection
- Nest software prioritizing efficiency over comfort
- W2 or AUX wire not properly connected at thermostat
Most fixes happen in the first 3 steps.
Running Emergency Heat continuously for extended periods will dramatically increase your electricity bill. Emergency heat uses electric resistance strips that consume 3 to 5 times more energy than a heat pump. Use it only as a temporary solution.
Tools & Requirements
These tools will help you complete this fix.
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Step-by-Step Solution
Change Heat Pump Balance
Open the Nest app go to thermostat settings then Heat Pump Balance. Change it from Max Savings or Balanced to Max Comfort. The Max Savings setting aggressively prevents auxiliary heat from running to save energy but this means your home may never reach the set temperature in cold weather. Max Comfort allows the Nest to use auxiliary heat whenever the heat pump alone cannot keep up.
Check Lockout Temperature
In Nest settings look for the Aux Heat Lockout temperature. This is the outdoor temperature below which the Nest allows auxiliary heat to run. If this is set too low like 20 degrees the aux heat will not activate until it is extremely cold outside. Set it to a higher threshold like 35 to 40 degrees so auxiliary heat can supplement the heat pump during moderately cold weather when the pump struggles.
Verify Wiring Configuration
Go to Nest settings then Equipment then Wiring. Confirm that the W2 or AUX wire is detected and shows as connected. If it shows as not connected the physical wire may have slipped out of the Nest base terminal. Pull the Nest display off the base and check that the wire labeled W2 or AUX is firmly inserted into the correct terminal and the tab is pushed down to secure it.
Check O/B Wire Orientation
The O/B wire controls the heat pump reversing valve. If configured incorrectly the Nest may run the heat pump in cooling mode when trying to heat. Go to Equipment settings and check whether O/B is set to energize on Cool or energize on Heat. Most systems use energize on Cool which is the Nest default. If your system is different consult your HVAC installer or heat pump documentation.
Use Emergency Heat Manually
If your home is dangerously cold you can force emergency heat immediately. On the Nest go to Settings then Equipment then Emergency Heat and toggle it on. This bypasses the heat pump entirely and runs only the auxiliary electric heat strips or gas furnace backup. Use this as a temporary measure while troubleshooting. Remember to turn it off when normal heating is restored as emergency heat is significantly more expensive to run.
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.
After changing Heat Pump Balance to Max Comfort monitor your energy usage in the Nest app for a month. The increase in auxiliary heat usage is typically modest and well worth the comfort improvement in cold weather. **Product Intelligence:** - C-wire required for most models - 2.4GHz WiFi only - Nest Aware subscription for history
Thermostat issues that keep returning are often caused by stale backup-battery memory holding old settings across power cycles without the user realising.
- Nest Heat Pump Balance set to Max Savings
- Auxiliary heat lockout temperature set too low
- O/B wire configured incorrectly for heat pump system
- Nest not detecting aux heat wire connection
- Nest software prioritizing efficiency over comfort
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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