Honeywell / Resideo VisionPRO 8000 with Wi-Fi touchscreen thermostat (TH8321WF1001): quick sheet

Covers: VisionPRO 8000 Smart / with Wi-Fi, TH8321WF1001: up to 3 heat / 2 cool heat pump or 2 heat / 2 cool conventional, with one universal IAQ output (U1) and a wired sensor input (S1). Distributors list it as discontinued; many are still in the field. RedLINK versions (TH8320R / TH8321R) are related but not covered here.

Single sourceBrands: Honeywell Home / Resideo3 components

Pro touchscreen with C-wire power required, separate R and Rc, an L/A output, U1 dry-contact IAQ relay, S1 sensor input and a password-protected installer setup (the password is the date code). Calls: Wi-Fi/Total Connect Comfort registration, wrong IAQ setup on U1, outdoor temperature source, and two-transformer jumper errors.

Safety first

24 VAC only.
Power off before rewiring; never bridge two transformers.

How it works

24 VAC with a C wire is required. Remove the factory R-Rc jumper only on two-transformer systems; C then comes from the cooling transformer.

Heat pump terminals: O/B (set O or B in setup), Aux/E (backup/emergency heat), Y/Y2, G and L/A (heat pump reset/equipment monitor). Conventional: W/W2, Y/Y2, G, A.

U1/U1 is a dry-contact IAQ relay for a humidifier, dehumidifier, ventilator or an extra heat/cool stage; it can be set normally open or closed. A field jumper from R to U1 is used only when the device is powered by the system transformer.

S1/S1 takes a wired indoor, outdoor or discharge air sensor (10k ohm NTC sensors are listed as accessories). Outdoor temperature can come from that sensor or from the internet.

K terminal works with Honeywell's C-wire adapter (Y and G on one wire) when only four wires are available.

Installer setup and installer test: Menu > Installer Options > enter the date code as the password. The date code is on the back of the thermostat or under Menu > Dealer Information.

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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

Thermostats: alerts and wiring codes vs real equipment faults (Nest, ecobee, Honeywell, communicating systems)

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7 steps ~20 mineasy

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5 steps ~15 mineasy

Guide · Thermostat

R, Rh and Rc: when to keep the jumper and when a system has two transformers

Most forced-air systems have one 24 V transformer at the furnace or air handler, and R and Rc are tied together (a factory jumper or an internal link in the thermostat). Some homes, usually a boiler or older furnace for heat plus a separate air handler or add-on AC, have two transformers: one for heat on Rh/R and one for cooling on Rc. Joining two transformers through the thermostat can blow fuses or burn transformers. Decide which you have before landing wires, and pick a thermostat that supports separate Rh and Rc when there are two.

5 steps ~30 minmoderate

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

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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.

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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.

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