Honeywell T4 Pro ISU Menu: Complete Installer Setup Guide
The Honeywell T4 Pro ISU menu controls how the thermostat operates after installation, but heating or cooling may not respond when this setup is skipped or configured incorrectly. This issue is common on the TH4110U2005, where the system type must match the actual equipment.
The TH4110U2005 is the most common T4 Pro model used in standard systems. For installation and wiring details, see the Honeywell T4 Pro thermostat manual.
Quick Answer
The Honeywell T4 Pro ISU menu is the installer setup menu used to configure system type, reversing valve behaviour, fan control, and compressor protection. To access it, press and hold the Center button and the + button for about 3 seconds, then select ISU from the advanced menu. The most critical setting is ISU 200, which must match your actual HVAC equipment type.
- T4 Pro ISU Settings at a Glance
- What's the Honeywell T4 Pro ISU Menu?
- How the T4 Pro Installer Setup Menu Works
- How to Access the Honeywell T4 Pro Installer Setup Menu
- Why Some T4 Pro ISU Settings Do Not Appear in the Menu
- ISU Group 100: Display and Scheduling Settings
- ISU Group 200: Heating System Settings (Most Critical)
- How to Identify Your System Type for ISU 200
- ISU Group 300: System Changeover Settings
- ISU Group 365: Cycle Rate Settings
- ISU Group 400: Protection and Comfort Settings
- ISU Group 700: Filter Reminder Settings
- ISU Group 1400: Display and Clock Settings
- When to Use the Temperature Offset at ISU 1420
- Recommended Settings for Common Installations
- The Five ISU Settings Most Installers Get Wrong
- What the Manual Tells You to Check First
- How to Reset the T4 Pro ISU Menu to Factory Defaults
- Download the Honeywell T4 Pro Installation Manual
- An Installer's Perspective on the T4 Pro ISU Menu
- FAQ's
- Conclusion
T4 Pro ISU Settings at a Glance
The table below covers the six settings most likely to affect whether your system heats and cools correctly. Full details for every setting follow in the sections below.
| ISU Number | Setting Name | Why It Matters |
|---|---|---|
| ISU 120 | Scheduling options | Sets whether the thermostat is programmable and which format |
| ISU 200 | Heating system type | Most critical setting — must match your actual HVAC equipment |
| ISU 218 | O/B reversing valve | Heat pump only — wrong setting causes heating and cooling to reverse |
| ISU 230 | Heat fan control | Determines whether thermostat or equipment controls the blower |
| ISU 300 | System changeover | Sets whether Auto mode is manual or automatic |
| ISU 387 | Compressor protection | Prevents short cycling — should stay at default 5 minutes |
What’s the Honeywell T4 Pro ISU Menu?
The Honeywell T4 Pro ISU menu is the installer setup configuration system used to match the thermostat with the HVAC system it controls. It allows technicians to configure heating system type, reversing valve behaviour, fan control, cycle rates, and temperature display settings.
ISU stands for Installer Setup. The ISU menu does not control daily temperature or scheduling. It controls the relationship between the thermostat and the HVAC equipment behind the wall. The menu can be re-entered after installation at any time without losing programming data.
What does ISU stand for on a Honeywell thermostat?
ISU stands for Installer Setup. It is the built-in configuration menu that allows a technician to match the thermostat to the specific type of HVAC equipment it controls.
Which ISU setting is most important on the T4 Pro?
ISU 200 is the most important setting. It tells the thermostat whether the system is conventional forced air, a heat pump, radiant heat, or steam. An incorrect value here prevents the system from heating or cooling at all.
How many ISU settings does the T4 Pro have?
The T4 Pro has over 20 individual ISU settings organised across several groups. Most residential installations only require changes to two or three settings, with the remaining settings left at factory defaults.
The T4 Pro belongs to the Honeywell Home Pro Series product line manufactured by Resideo Technologies. The most common T4 Pro model for US residential installations is the TH4110U2005. You need the ISU menu when installing for the first time, replacing an older thermostat, correcting heating or cooling behavior after installation, or configuring a heat pump. Before entering the ISU menu, see the full Honeywell T4 Pro thermostat manual for wiring diagrams and terminal guidance.
How the T4 Pro Installer Setup Menu Works
The T4 Pro installer setup menu shows configuration options as numbered codes called ISU numbers. Each ISU number controls one specific system behaviour. Use the plus and minus buttons to change a value and select to move to the next setting. The menu hides settings that do not apply to your current configuration. This is normal and not a fault. Heat pump settings only appear after ISU 200 is set to Heat Pump.
How to Access the Honeywell T4 Pro Installer Setup Menu
⚠ Warning Before Changing ISU Settings
Changing installer settings incorrectly can cause the thermostat to control the wrong equipment or prevent the system from heating or cooling. If you are unsure about your HVAC system type, check the system wiring or consult the installation manual before modifying any ISU settings.
The ISU menu is accessed through the advanced menu using the same button sequence on all TH4110U2005 units.
Button Sequence
- Press and hold the Center button and the + button at the same time for approximately 3 seconds.
- The display shows the advanced menu. ISU will appear as one of the options.
- Press Select to enter the ISU menu.
- Use + or minus to view available values for the current setting.
- Press + or minus to change the value of the currently displayed setting.
- Press Select to confirm the current value and advance to the next setting.
- Press Back to return to the previous setting without changing it.
- Press Home when finished. All selected values are saved automatically.
Why Some T4 Pro ISU Settings Do Not Appear in the Menu
The T4 Pro installer setup menu uses conditional logic. It hides settings that do not apply to your current system configuration. This is the most common source of confusion during T4 Pro installation.
The most important example is the ISU 218 for the reversing valve. This setting only appears in the menu after ISU 200 is set to 2 (Heat Pump). If ISU 200 is set to 1 (Conventional), the thermostat hides all heat pump specific settings, including ISU 218. If you cannot find ISU 218 in your menu, check ISU 200 first. This behaviour is normal and is documented in the official Resideo installation guide.
The same logic applies to ISU 205 and ISU 303 — both only appear under specific ISU 200 configurations. Always set ISU 200 before looking for any other Group 200 settings.
Navigating Between Settings
Not all ISU numbers appear in sequence. The menu skips numbers that do not apply to your current configuration. If the menu jumps from ISU 200 to ISU 230, that is correct for a conventional forced air system where heat pump settings are hidden.
Saving and Exiting
Press Home at any point to save all changes and return to the home screen. There is no separate save prompt. If you press Back repeatedly without pressing Home, changes to the last viewed setting may not be saved.
ISU Group 100: Display and Scheduling Settings
Group 100 settings control how the thermostat displays temperature and what scheduling options are available to the homeowner. These settings do not affect heating or cooling equipment directly.
| ISU | Name | Options | What to Set |
|---|---|---|---|
| 120 | Scheduling options | 0=Non-programmable, 2=5-2, 3=5-1-1 (default), 4=7-day | Match your preferred schedule format. Set to 0 if no schedule needed. |
| 125 | Temperature scale | 0=Fahrenheit (default), 1=Celsius | Match homeowner preference |
ISU Group 200: Heating System Settings (Most Critical)
Group 200 is the most important section of the T4 Pro ISU menu. ISU 200 tells the thermostat what type of heating system it controls. An incorrect entry here causes the thermostat to send the wrong signals to the equipment. Set ISU 200 before any other setting in this group.
| ISU | Name | Options | What to Set |
|---|---|---|---|
| 200 | Heating system type | 1=Conventional forced air (default), 2=Heat pump, 3=Radiant heat, 5=Cool only | Must match your actual system. Wrong value causes complete failure to heat or cool. |
| 205 | Heating equipment type | 1=Standard gas, 2=High efficiency gas, 3=Oil, 4=Electric, 7=Air-to-air heat pump, 8=Geothermal, 9=Hot water radiant, 12=Steam | Select the closest match. Option 12 applies to older steam radiant systems. Check your equipment documentation if unsure. |
| 218 | Reversing valve O/B | 0=O energised in cool (default), 1=B energised in heat | Only appears when ISU 200 is set to Heat Pump. Most systems use O. Trane and American Standard typically use B. |
| 220 | Cool stages | 0=None, 1=Single stage (default) | T4 Pro supports single stage cooling only. |
| 221 | Heat and backup stages | Heat: 1 stage only. Backup: 1 stage only. | T4 Pro supports single stage heating only. No two-stage option available. |
| 230 | Heat fan control | 1=Equipment controls fan, 2=Thermostat controls fan (default) | Use 2 for most systems. Use 1 for systems with their own fan control board. |
How to Identify Your System Type for ISU 200
If you are replacing an existing thermostat, check the old wiring. If the O/B terminal had a wire connected, your system is a heat pump. If only R, W, Y, G, and C terminals were used with no O/B wire, your system is conventional forced air. If you have panel or baseboard radiators with no forced air, your system is radiant. If the system uses pipes, a boiler, and steam, set ISU 200 to 3 (Radiant Heat), then set ISU 205 to 12 (Steam). Steam systems are common in US homes built before 1960.
ISU Group 300: System Changeover Settings
Group 300 controls how the thermostat switches between heating and cooling modes. For most residential installations only ISU 300 needs to be changed. ISU 303 only applies when ISU 300 is set to automatic.
| ISU | Name | Options | What to Set |
|---|---|---|---|
| 300 | System changeover | 0=Manual (default), 1=Automatic | Set to 1 to enable Auto mode on the thermostat display |
| 303 | Auto changeover differential | 0 to 5 degrees F (default 0) | Only applies when ISU 300 is set to Automatic. Sets minimum degree difference before mode switches. |
ISU Group 365: Cycle Rate Settings
Cycle rate settings control how many times per hour the thermostat allows the heating or cooling equipment to cycle on and off. This section is unique to the T4 Pro and does not exist on the T6 Pro. A cycle rate that is too high causes short cycling — the system turns on and off too quickly, increasing wear on the compressor and heat exchanger. Leave ISU 365 and 370 at default unless your equipment documentation recommends otherwise.
| ISU | Name | Options | What to Set |
|---|---|---|---|
| 365 | Cool cycle rate | 1 to 6 cycles per hour | Default is 3. Lower values reduce short cycling. Higher values maintain temperature more precisely but increase wear. Leave at default for most systems. |
| 370 | Heat cycle rate | 1 to 12 cycles per hour (also applies to auxiliary heat) | Default is 3 for heat. A value of 3 works for most gas furnaces. Electric systems can run higher. Check your equipment manual if unsure. |
ISU Group 400: Protection and Comfort Settings
Group 400 covers compressor protection, Adaptive Intelligent Recovery, temperature setpoint limits, and keypad lockout. Most can be left at factory defaults for residential installations.
| ISU | Name | Options | What to Set |
|---|---|---|---|
| 387 | Compressor protection | 0=Off, 1 to 5 minutes (default 5) | Leave at default 5 minutes. Turning this off risks compressor damage from short cycling. |
| 425 | Adaptive Intelligent Recovery | 0=No, 1=Yes (default) | Leave on. AIR starts heating or cooling early so the room reaches setpoint on schedule. |
| 430 | Minimum cool setpoint | 50 to 99 degrees F (default 50) | Prevents accidental cooling setpoints below this value |
| 431 | Maximum heat setpoint | 45 to 90 degrees F (default 90) | Prevents accidental heating setpoints above this value. Note: T4 Pro minimum is 45F, not 40F as on T6 Pro. |
| 435 | Keypad lockout | 0=None (default), 1=Partial, 2=Full | 0=No lock, 1=Partial lock, 2=Full lock |
ISU Group 700: Filter Reminder Settings
Group 700 settings configure air filter replacement reminders. These are optional and do not affect heating or cooling operation. Setting a reminder is useful for rental properties where the owner may forget routine maintenance.
| ISU | Name | Options | What to Set |
|---|---|---|---|
| 702 | Number of air filters | 0 (default), 1, or 2 | Set to match how many air filters your system has. Enables filter reminder alerts. |
| 711 | Air filter 1 replacement reminder | 0=Off (default), 1=10 run days, 2=20, 3=30, 4=45, 5=60, 6=90, 7=120, 8=150 run days, 9=30 calendar days, 10=45, 11=60, 12=75 calendar days, 13=3 months, 14=4, 15=5, 16=6, 17=9, 18=12, 19=15 calendar months | Set based on your filter manufacturer recommendation. Most 1-inch filters need replacement every 30 to 90 days. |
| 712 | Air filter 2 replacement reminder | Same options as ISU 711 | Only applies if ISU 702 is set to 2 |
ISU Group 1400: Display and Clock Settings
Group 1400 settings control the thermostat display backlight, brightness, clock format, daylight saving time, and temperature calibration offset. This group is unique to the T4 Pro and does not exist on the T6 Pro.
| ISU | Name | Options | What to Set |
|---|---|---|---|
| 1400 | Backlight mode | 0=On demand (default), 1=Continuous | Set to 0 to save battery life on batteries. Set to 1 for continuous backlight when C-wire is connected. |
| 1401 | Backlight brightness | 1 to 5 (default 3) | Adjust to match room lighting. Higher values use more power. Useful when thermostat is in a dim hallway. |
| 1410 | Clock format | 12=12-hour clock (default), 24=24-hour clock | Match homeowner preference |
| 1415 | Daylight saving time | 0=Off, 1=On (default) | Leave on for most US installations. Turn off only if the homeowner manually adjusts the clock. |
| 1420 | Temperature offset | -3 to +3 degrees F (default 0) | Use only if thermostat reads consistently high or low compared to a calibrated thermometer. Each increment adjusts by 1 degree F. |
When to Use the Temperature Offset at ISU 1420
Use ISU 1420 only if the thermostat consistently reads higher or lower than a calibrated thermometer nearby. Place a reference thermometer next to the thermostat for 15 minutes. If it reads 2 degrees high, set the offset to minus 2. Fix placement problems like direct sunlight or drafts first — an offset will not correct those.
Recommended Settings for Common Installations
The tables below show recommended starting values for the two most common T4 Pro installation types based on official Resideo documentation.
Conventional Forced Air System
| ISU | Setting | Recommended Value | Reason |
|---|---|---|---|
| 200 | Heating system type | 1 = Conventional | Match your forced air furnace |
| 120 | Scheduling | 3 = 5-1-1 or 4 = 7-day | Match homeowner preference |
| 230 | Heat fan control | 2 = Thermostat controls fan | Correct for most gas and electric furnaces |
| 387 | Compressor protection | 5 minutes | Protects cooling equipment |
| 425 | Adaptive Intelligent Recovery | 1 = Yes | Improves comfort |
| 300 | System changeover | 1 = Automatic | Enables Auto mode on display |
| 365 | Cool cycle rate | 3 | Standard residential setting |
| 370 | Heat cycle rate | 3 to 5 for gas, higher for electric | Match equipment specification |
Heat Pump System (Single Stage)
| ISU | Setting | Recommended Value | Reason |
|---|---|---|---|
| 200 | Heating system type | 2 = Heat pump | Required for heat pump operation |
| 205 | Heating equipment type | 7 = Air-to-air heat pump | Match your equipment |
| 218 | Reversing valve O/B | 0 = O energised in cool | Correct for most brands. Trane/American Standard use 1. |
| 220 | Cool stages | 1 = Single stage | T4 Pro supports single stage only |
| 300 | System changeover | 1 = Automatic | Required for heat pump Auto mode |
| 303 | Auto changeover differential | 3 degrees F | Standard starting value |
| 387 | Compressor protection | 3 to 5 minutes | Do not set below 3 minutes on a heat pump |
| 365 | Cool cycle rate | 3 | Standard residential setting |
The Five ISU Settings Most Installers Get Wrong
These five errors account for the majority of T4 Pro post-installation callbacks. Check each one before closing the installation.
| ISU Setting | Common Mistake | Correct Action |
|---|---|---|
| ISU 200 | Set to Conventional when system is a heat pump | Check outdoor unit. If it heats and cools it is a heat pump. Set to 2. |
| ISU 218 | Not visible — installer assumes it is missing | ISU 218 only appears after ISU 200 is set to Heat Pump. Set ISU 200 first. |
| ISU 230 | Left at Equipment Controls Fan for a conventional system | Most conventional systems need 2 = Thermostat Controls Fan |
| ISU 205 | Left at default when system is steam radiant | Change to 12 = Steam for steam heat systems. This is a T4 Pro exclusive option. |
| ISU 387 | Turned off during testing to speed up commissioning | Always restore to 5 minutes before leaving. Short cycling damages the compressor. |
What the Manual Tells You to Check First
Use this table when something is wrong after installation. Each symptom maps directly to an ISU setting.
| What You See | What the Manual Calls It | Where to Find It |
|---|---|---|
| System not heating or cooling after install | Incorrect system type | ISU 200 — verify heating system type |
| Heating and cooling modes are reversed | O/B valve setting error | ISU 218 — verify O or B matches heat pump |
| ISU 218 does not appear in menu | Conditional menu logic | Set ISU 200 to Heat Pump first, then ISU 218 appears |
| Fan runs continuously | Fan control setting | ISU 230 — check heat fan control setting |
| Cool On or Heat On flashing | Compressor protection delay | ISU 387 — normal, wait 3 to 5 minutes |
| Auto mode not available on display | Manual changeover setting | ISU 300 — set to 1 for automatic changeover |
| Temperature reads higher or lower than actual | Temperature calibration offset | ISU 1420 — adjust offset in 1 degree increments |
How to Reset the T4 Pro ISU Menu to Factory Defaults
If ISU settings were entered incorrectly and you want to start over, the T4 Pro supports a full factory reset. Enter the advanced menu by pressing and holding Center and + for 3 seconds. Navigate to Reset and press Select. Choose “Factory Reset” and confirm. This clears all ISU settings, schedules, and time settings. All ISU entries must be re-entered from the beginning after a factory reset.
A factory reset does not affect the wiring or the physical UWP wall plate. After resetting, re-enter the ISU menu and begin with ISU 200 before powering on the HVAC system. If you need broader troubleshooting after a reset, the Honeywell Thermostat Not Working guide covers system-level diagnostics.
What Happens After a Power Outage?
If the T4 Pro ISU settings reset after a power outage, the thermostat may return to default system type. This can cause incorrect heating or cooling behavior. Re-enter the ISU menu and confirm your system type and fan settings.
Download the Honeywell T4 Pro Installation Manual
You can download the official Honeywell T4 Pro Installation Instructions Guide free from Resideo. This document covers all wiring diagrams, terminal descriptions, and the complete ISU menu reference for the TH4110U2005.
An Installer’s Perspective on the T4 Pro ISU Menu
The T4 Pro catches installers off guard in two ways. The first is the conditional menu. Technicians used to the T6 Pro expect all ISU settings to be visible at once. On the T4 Pro, heat pump settings disappear completely when ISU 200 is set to conventional. This is normal, but it looks like a fault if you do not know to expect it.
The second surprise is the cycle rate settings at ISU 365 and 370. Most installers leave these at default and move on. That is correct for standard residential systems. But if a homeowner later reports short cycling or temperature swings, check these first. They do not exist on the T6 Pro and are not covered in most installation guides.
This article was reviewed for technical accuracy against the official Honeywell Home T4 Pro Installation Instructions Guide published by Resideo Technologies.
FAQ’s
Conclusion
The Honeywell T4 Pro ISU menu covers over 20 settings, but most residential installations require changes to three: ISU 200 for system type, ISU 218 for heat pump reversing valve direction, and ISU 120 for scheduling format. If ISU 218 does not appear in your menu, set ISU 200 to Heat Pump first. The cycle rate settings at ISU 365 and 370, and the display settings at Group 1400 can be left at factory defaults for most installations.
For a complete overview of the T4 Pro, including wiring diagrams and terminal guidance, see the full Honeywell T4 Pro thermostat manual. For a comparison across Pro Series models, see the Honeywell Pro Series thermostat guide.
