Honeywell Thermostat Warning Sign (Triangle With Exclamation Point)

“Is your Honeywell thermostat displaying a warning sign, a triangle with an exclamation point?

Don’t panic! In this troubleshooting guide, we’ll walk you through simple steps to decode the symbol and get your thermostat back to optimal performance in no time.”

A thermostat displaying a triangle with an exclamation mark is simply telling you that there is something with your system that needs attention.

This can be anything from  a dirty air filter that needs a replacement to a critically low  battery.

It can be hard to tell exactly what the issue is until you manually check the code that is triggering the warning sign.

To check the underline code behind the warning sign, follow these steps below:

Step 1: The alert icon appears on the Home screen.

Step 2: Press Menu, and then press until the display shows ALRT.

Step 3: Press ‘Select’  to display which alert(s) are present.

Step 4: The message REPL (REPLACE AIR FILTER) appears.

Not that the  reminder can be snoozed or cleared. But it’s  recommendable to change the air filter before clearing the reminder.

To snooze the reminder, press ‘Select’. The word SNZE (SNOOZE) appears.

  •  Press Select again to snooze the reminder for 7 days.

To clear, press Select, and then press to go to CLER (Clear).

  •  Press Select to clear the air filter reminder

 The following table shows some of the codes that can trigger the triangle symbol with exclamation point.

164Heat pump needs service
170Internal Memory Error
173Thermostat thermostat temperature sensor Error
181Replace Air Filter 
405Low battery
407Critically low battery


Heat pump needs service. This reminder is mostly based on the number of hours the HVAC system has been in use. It is not necessary that there is a need for service.

As a good rule of thumb it is recommended to service your HVAC system at least once a year. More, even better.

During annual tune ups, the technicians will also perform preventive measures to prevent your system from unforseen breakdowns

Read also: Honeywell Thermostat Symbol Meanings Explained


The memory of the thermostat has encountered an error. Please contact dealer for assistance


The sensor of the thermostat has encountered anerror. Please contact dealer to replace the Thermostat


Replace air filter. The timer however has no idea on the status of your air filter. It is just programmed to alert after a certain number of hours. 

I would advise you to start by replacing your air filter before you reset the reminder.

After you have replaced your filter,  reset the timer by touching the “dismiss” button on the thermostat screen after it is replaced.

Read also: Honeywell thermostat filter reset


This code means that the batteries are getting low. You need to replace your thermostat batteries at least once a year.

But when you see this code on your thermostat, you should replace them within two months.


With this code, your thermostat batteries are nearly dead and you should replace them  as soon as possible.  Get high quality batteries from a known manufacturer.

Final thoughts

In conclusion, encountering a warning sign on your Honeywell thermostat in the form of a triangle with an exclamation point shouldn’t cause panic.

 It is a way for your thermostat to communicate that there is an issue with your system that requires attention.

By following the troubleshooting steps outlined in this guide, you can identify the specific problem behind the warning sign and take appropriate action.

Read also: Honeywell Thermostat Low Battery Symptoms And How to Replace Batteries

Remember that the underlying issue could be something as simple as a dirty air filter or low battery levels.

Regular maintenance, such as replacing the air filter and thermostat batteries, can help ensure optimal performance and prevent potential problems.

Additionally, understanding the various codes associated with the warning sign enables you to determine the nature of the issue.

Some codes may indicate the need for professional assistance, such as heat pump servicing or thermostat sensor replacement.

More resources here

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