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What different HVAC monitoring alerts mean

Your Nest thermostat can help identify potential issues with your eligible heating, ventilation and air conditioning (HVAC) systems. If a potential issue is detected, we’ll send you an HVAC monitoring alert via email or a Google Home app notification.

If you received an alert, check the list below to learn about the potential issue and the data used to identify it. You’ll also find some examples of specific problems to check for.

Learn more about Google Nest HVAC monitoring alerts.

Important: Nest HVAC monitoring is not meant to replace the diagnosis of a qualified HVAC professional. We make no endorsement, representation, or warranty about the health of your HVAC system. You may still experience issues with your HVAC system that we don't alert you to.

Urgent alerts

Urgent alerts tell you about serious issues that you should address right away. You may want to address the issue yourself, but you can also get HVAC pro assistance

This image is an example of an urgent alert. 

You may receive one of the following urgent alerts:

Your heating system failed to heat your home

You’ll receive this alert if Google Nest has identified a time when your heating system didn’t appear to be working.

It identifies heating failures by monitoring changes in your indoor temperature while your system is heating. If those changes are different than what Google Nest expects, we’ll send an alert.

If your heater is on but your home isn’t getting warmer, your heating system’s fan may have a problem. Or, if you have a gas or oil furnace, you may have a dirty or faulty flame sensor that for safety reasons prevents the gas from burning.

Your A/C system failed to cool your home

You’ll receive this alert if Google Nest has identified a time when your A/C system didn’t appear to be working. 

It identifies cooling failures by monitoring changes in your indoor temperature while your system is cooling. If those changes are different than what Google Nest expects, we’ll send an alert.

If your air conditioner is on but your home isn’t getting cooler, your A/C system’s compressor, indoor fan, or outdoor fan may have a problem, or your startup capacitor may be broken. You may be able to check the capacitor by listening for clicking noises in the outdoor unit that indicate it’s trying to start but doesn’t succeed.

Note: You may also receive this alert in some special cases when your A/C system is working as expected. If you’ve enrolled in a demand response utility program, it may cut off power to the compressor on very hot summer days. This power loss will cause the alert to be sent. Also, if your Y1 wire is connected to a fan, which doesn’t cool your home, you may receive the alert.

Furnace shutdown

You’ll receive this alert if Google Nest has identified times when the heater was on, and electrical power to the thermostat was lost. This power loss may indicate a serious problem.

Furnaces typically have a safety switch that shuts off power to part of the system if the air inside the furnace gets too hot. The furnace may get too hot because not enough air is flowing through the system due to issues such as a dirty filter, restrictive ductwork, or a problem with the fan.

Your heating system may still work, but these high temperatures and continuous shifts between on and off can damage your furnace and cause a safety hazard. For example, the heat exchangers may develop cracks that are expensive to fix and that may allow carbon monoxide to leak into your home.

Learn more about how to troubleshoot a furnace shutdown (heads-up) alert.

Early warnings

Early warnings tell you about issues that you should address soon. You may want to address the issue yourself, but you can also get HVAC pro assistance. 

This image is an example of an early warning.

You may receive one of the following early warnings:

Your system briefly stopped heating your home several times

You’ll receive this alert if Google Nest has identified multiple times when your heating system appears to have stopped heating your home for a period in the middle of the heating cycle. It identifies these times from data about when the reported indoor temperature went down temporarily while the thermostat was telling your heating system to heat your home.

Heating systems that burn fossil fuels, like gas, may turn off your furnace briefly if a safety mechanism correctly or mistakenly identifies a potential problem.

Your system’s safety mechanisms are designed to shut down your furnace to prevent severe problems like gas or carbon monoxide leaks, fires or explosions in your home. You may experience short shutdowns if a problem, such as an igniter failure, happens intermittently. But if something is wrong with the mechanism itself, it may also briefly turn off the gas as a safety precaution. For example, a flame sensor should make sure your gas is burning properly. If the sensor gets dirty and has trouble detecting a flame, it will stop your furnace from burning gas.

In cases like a dirty flame sensor, most of the time your heating system will turn back on by itself, and you won’t know about the problem until it becomes more serious. This early warning alert can help you address the problem while it’s less serious.

Your A/C system briefly lost power several times

You’ll receive this alert if Google Nest has identified multiple times when your A/C system lost power.

Your A/C system should not lose power during normal operation. If it loses electrical power, it may have a problem.

Your A/C system both cools and removes moisture from your home. The moisture that your system removes condenses into water that needs to be drained, as much as 5-20 gallons per day.

A/C systems are designed to drain this water, but sometimes it may have problems. For example, the pump may fail or the drain line may become clogged. A mechanism, such as a float switch, shuts down the system if it detects that the water isn't draining properly. In some cases, the problem may be the switch itself.

Your A/C ran longer than expected

You’ll receive this alert if Google Nest has determined that your A/C system does not behave as expected while cooling your home to a comfortable temperature.

If your A/C system does not behave as expected, it may have a problem. For example, your system may have low refrigerant levels, air flow problems, or frost building on the evaporator coils.

Your system may still work with these conditions, but it may cost you more than necessary to cool your home and may cause more damage in the long run.

Your heat pump isn't working properly

You’ll receive this alert if Google Nest determines that your heat pump may have used its backup auxiliary heat more than expected. When it’s very cold, your heat pump will use auxiliary heat to help heat your home. This may use more energy, but will help heat your home quicker. However, if your heat pump’s compressor, the main source for your system’s heating, is performing poorly when the weather is warmer, your auxiliary heat will still be used to help heat your home when it otherwise might not be needed. 

Google Nest looks at how much your system uses this extra help from auxiliary heat to determine if you could have a problem. This is measured by using the outdoor temperature and the heating runtimes from your thermostat. 

If we detect an issue during the heating season this could continue to have an impact during the cooling season since your heat pump provides both heating and cooling to your home.

While your auxiliary heat will help heat your home when it’s cold, it won’t assist your compressor in cooling when it’s hot.This means your heat pump may seem to work fine in the winter, but it could still have issues in the summer when you try to cool your home.

Filter reminders

You’ll receive this alert if you may need to replace your filter soon. 

In a forced-air HVAC system, air filters can help remove dust and other particles when recirculating air in your home. They can also help prevent dirt from entering the fan and other parts of the system. 

Filters get dirty over time and need to be replaced. Otherwise, they can cause your system to run less efficiently or even damage it. For example, reduced air flow from dirty filters can cause your furnace to overheat or ice to form on your A/C system’s evaporator coils. 

Your Nest thermostat can monitor how long your system’s fan has been running. After a specified amount of time, it will remind you to replace the filter. 

Learn more about air filters and your Nest Thermostat.

Learn how to manage HVAC monitoring settings and what to do when you get an alert.

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