- 01Match exact T6/T9/T10
- 02Use that model’s table
- 03Distinguish compressor/backup
T6 Pro Smart
The Professional Install Guide 33-00392 covers TH6220WF2006 and TH6320WF2003. It documents holding Menu for 5 seconds to reach the Advanced Menu. This is an identification aid, not permission to alter commissioning.
| Item | Meaning in this guide |
|---|---|
| ISU 355 Balance Point / Compressor Lockout | Restricts the heat pump below the selected outdoor condition. Listed range Off or 5–60°F. The guide distinguishes a 40°F dual-fuel default for air-source gas/oil backup from Off for electric backup or geothermal. |
| ISU 356 Aux Heat Lock Out | Restricts backup above the selected outdoor condition. Listed range Off or 5–65°F; available only with the relevant heat-pump/auxiliary configuration and outdoor-temperature input. |
A listed default is not the right temperature for every home. Compare the installed fuel/configuration with the guide before even interpreting a number.
T6 Pro II
The official T6 Pro II ISU table uses ISU 355 Compressor Lockout / Balance Point and ISU 356 Outdoor Lockout Backup Heat. It notes a wired-sensor requirement for the specified TH6320U/TH6220 compressor-lockout configuration. Do not use the T6 Pro Smart entry gesture or assume internet weather on this different model.
T10 and T10+ Pro
The official ISU table groups equipment lockouts under ISU 3120. It lists Compressor Lockout / Balance point from Off or −15°F to 50°F, and Backup Heat Lockout from Off or 5°F to 65°F. These are separate restrictions, not two names for one “best temperature.”
The Advanced Features page documents manual Emergency Heat under Menu → System Mode for a configured heat pump with backup. In that mode the heat pump is locked out. A system can intentionally be in backup-only operation; silence at the outdoor unit is not a stand-alone fault diagnosis.
T9 Smart
The T9 User Guide 33-00478 describes Menu → system Mode, with Emergency Heat available when configured for a heat pump with backup. The checked user and installation guides do not establish an auxiliary-lockout ISU comparable to the T6 or T10 values above. This page deliberately supplies no guessed T9 ISU number.
Take a record, not a new setting
- Write the full model, including Smart/II/plus suffixes.
- Record current mode, installed backup fuel, alert text and existing lockout values without changing them.
- Ask which sensor/weather input and commissioned control strategy apply.
- If the home is getting colder or a hazard is suspected, seek appropriate help rather than experimenting with installer options.
These guide-specific limits were rechecked on November 13, 2026. Use the linked source if a later revision or installed configuration differs. The situation checklist does not select values for any Honeywell Home model.