Air-source heat pump outdoor unit beside a house in the snow
6 components covered

Field manual · Thermostat

Honeywell Home FocusPRO N100 non-programmable thermostats (TH1110U4000, TH1210U4001, TH1320U4002): quick sheet

Covers: FocusPRO N100 series on the UWP wall plate: TH1110U4000 (1H/1C, heat pump without aux), TH1210U4001 (heat pump 1 compressor + aux, or 1H/1C conventional, dual fuel), TH1320U4002 (heat pump up to 2 compressor stages + aux, up to 2H/2C conventional, dual fuel). Successor family to the older FocusPRO 5000/6000 contractor thermostats.

Cross-checkedBrands: Honeywell Home, Resideo6 components

A plain contractor-grade non-programmable thermostat that runs on 24 VAC or 2 AA batteries and is configured entirely by numbered installer setup (ISU) codes. The heat-pump models accept a wired outdoor sensor for balance point and aux lockout, which makes them a good cheap fix for heat pumps that run strip heat too much. Most problems are ISU mistakes.

Safety first

  • Power off before wiring
  • 24 V and millivolt only; never line voltage

How it works

Enter ISU by holding the bottom-left button and the Up arrow together for about 5 seconds. Up/Down changes a value, NEXT moves to the next ISU, SAVE ends. A new thermostat enters ISU on its own at first power-up.

Key ISUs: 2000 heating system type (1 conventional forced air, 2 heat pump, 3 radiant, 5 cool only); 2010 equipment type (for heat pumps 7 air-to-air, 8 geothermal); 2060 reversing valve (0 = O, energized in cool, default; 1 = B, energized in heat); 2070 compressor stages; 2071 heat / backup heat stages; 2180 backup heat source (31 electric default, gas/oil options for dual fuel).

Heat pump control: 3090 backup heat droop (Comfort, or 2-15°F), 3110 upstage timer for backup heat, 3120 compressor lockout / balance point (needs outdoor sensor), 3121 outdoor lockout for backup heat (5-65°F), 2175 drive Aux and E together or independently.

3240 compressor protection gives a minimum off time of 0-5 minutes (default 5). The Cool/Heat indicator may flash while it times out; that is not a fault.

Outdoor sensor C7089U1006 wires to the S terminals on the TH1210U4001 and TH1320U4002 (ISU 1060 = 1). It is used for lockouts only and is not shown on the display.

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Official manufacturer documentation

Always confirm values against the tech sheet for the exact model.

OnCall Tech is a reference tool for trained technicians and can make mistakes. Always disconnect power and confirm with the manufacturer's documentation before you work. © 2026 OnCall Tech. Original content; not a reproduction of any manufacturer document.Generic part photos (not of this brand): Air-source heat pump outdoor unit beside a house in the snow by PeterEastern, CC BY-SA 4.0

Diagnostic guides for this appliance

Guide · Thermostat

Furnace / air handler 3 A low-voltage fuse keeps blowing (finding the 24 V short)

A blown 24 V fuse is a symptom of a short in the thermostat wire, outdoor unit wire or a load (contactor coil, damper, humidifier). Isolate circuits one at a time instead of replacing fuses.

8 steps ~60 minmoderate
Guide · Thermostat

Zoned system: one zone not heating or cooling (damper and zone panel checks)

If only one zone fails, the cause is almost always that zone's damper, actuator, thermostat or wiring, not the furnace or AC. Simulate a call at the panel and check whether the damper actually moves.

8 steps ~45 minmoderate
Guide · Thermostat

Field pattern: thermostat replaced, now nothing works or the wrong thing runs (fuse, system type, O/B)

Almost every post-install failure comes from one of four things: a 24 V short during install that blew the board fuse, a missing C wire, the wrong equipment type in the installer menu, or the O/B (reversing valve) setting reversed. The wrong turn is assuming the new thermostat is defective or that the furnace failed the same day; check the install before ordering anything.

7 steps ~40 mineasy

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Google Nest Thermostat (2020, mirror face, no ring): quick sheet

Google Nest Thermostat launched October 2020 (model G4CVZ, sold as GA01334-US and color variants). Not the Nest Learning Thermostat (3rd/4th gen) or the Nest Thermostat E, which have their own sheets/notes.

9 components5 common failuresGoogle Nest
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ecobee3 lite smart thermostat (EB-STATE3LT-02 and Pro EB-STATE3LTP-02): quick sheet

ecobee3 lite retail (EB-STATE3LT-02) and contractor/Pro version (EB-STATE3LTP-02). Now listed as discontinued by several distributors but very common in the field. ecobee Premium/Enhanced have their own sheet.

9 components5 common failuresecobee
Manual · Thermostat

Honeywell Home T5 / T5+ Smart Thermostat (RCHT8610WF, RCHT8612WF, RTH8800WF): quick sheet

Honeywell Home / Resideo T5 Smart Thermostat RCHT8610WF (no C-wire adapter in the box), T5+ RCHT8612WF (ships with the THP9045A C-wire adapter) and RTH8800WF retail variant. T6 Pro, T9 and T10 have their own sheets.

7 components5 common failuresHoneywell Home, Resideo
Honeywell Home FocusPRO N100 non-programmable thermostats (TH1110U4000, TH1210U4001, TH1320U4002): quick sheet · OnCall Tech