Name: Manual for T3 Pro - Troubleshooting and error codes + PDF Download
Brand: Honeywell

Manual for T3 Pro - Troubleshooting and error codes + PDF Download

Brand: Honeywell

Category: Thermostat

Manual Type:

Language:

Uploaded: April 8, 2025, 1:46 p.m.

Manual Publish Date: 2020-04-01

Warranty Summary

None

To operate the Honeywell Home T3 Pro thermostat, users can navigate system modes by pressing the 'Menu' button and then the 'Mode (+)' button, choosing from Auto, Heat, Cool, Em heat (for heat pumps with auxiliary heat), and Off. Fan operation is controlled similarly using the 'Menu' and 'Fan (-)' buttons, with modes for Auto (fan runs only when heating or cooling) and On (fan always on). Installer setup (ISU) is accessed upon initial power-up or by pressing and holding the 'Menu' button for 5 seconds, allowing configuration of system settings through 'Edit (-)' and 'Next (+)' buttons, with options detailed in the manual.

Troubleshooting and error codes

Problem	Possible Causes and Solutions
Display is blank	Check circuit breaker and reset if necessary. Make sure power switch for heating & cooling system is on. Make sure furnace door is closed securely. Make sure fresh AA alkaline batteries are correctly installed (see page 2).
Heating or cooling system does not respond	Press Mode button to set system Heat (see page 5). Make sure the desired temperature is set higher than the inside temperature. Press Mode button to set system Cool (see page 5). Make sure the desired temperature is set lower than the inside temperature. Check circuit breaker and reset if necessary. Make sure power switch for heating & cooling system is on. Make sure furnace door is closed securely. Wait 5 minutes for the system to respond.
"Cool On" or "Heat On" is flashing	Compressor protection feature is engaged. Wait 5 minutes for the system to restart safely, without damage to the compressor.
Aux heat runs in cooling	For heat pump systems, verify there is not a wire attached to W on UWP systems. See "Wiring heat pump systems” on page 4.
Cool runs with a call for heat	For heat pump systems, verify there is not a wire attached to W on UWP systems. See “Wiring heat pump systems” on page 4.

Troubleshooting and error codes

Problem	Possible Causes and Solutions
Display is blank	Check circuit breaker and reset if necessary. Make sure power switch for heating & cooling system is on. Make sure furnace door is closed securely. Make sure fresh AA alkaline batteries are correctly installed (see page 2).
Heating or cooling system does not respond	Press Mode button to set system Heat (see page 5). Make sure the desired temperature is set higher than the inside temperature. Press Mode button to set system Cool (see page 5). Make sure the desired temperature is set lower than the inside temperature. Check circuit breaker and reset if necessary. Make sure power switch for heating & cooling system is on. Make sure furnace door is closed securely. Wait 5 minutes for the system to respond.
"Cool On" or "Heat On" is flashing	Compressor protection feature is engaged. Wait 5 minutes for the system to restart safely, without damage to the compressor.
Aux heat runs in cooling	For heat pump systems, verify there is not a wire attached to W on UWP systems. See "Wiring heat pump systems” on page 4.
Cool runs with a call for heat	For heat pump systems, verify there is not a wire attached to W on UWP systems. See “Wiring heat pump systems” on page 4.