Sensi Smart Thermostat Installation

• Small- and medium-tipped Phillips screwdrivers; optional wire cutter/stripper; a voltage tester; phone with the Sensi app.
• The 2.4 GHz Wi-Fi network name and password. Sensi is not compatible with 5 GHz-only networks.^[1][9]
• ST55 also uses 2 AA alkaline batteries for backup (not the primary power source).^[2]

1. Download the Sensi app, create an account, and tap + to add a thermostat. Choose Sensi smart thermostat for ST55 / 1F87U-42WF (the model is on the back of the faceplate).^[1]
2. If the new thermostat is not yet on the wall, choose “No, it needs to be installed” so the app walks the wiring.
3. With power off, remove the old cover. Photograph the old thermostat and the wiring — wire color does not always match the terminal letter.^[2]
4. Throw away jumper wires from the old thermostat. Sensi has an internal RC/RH jumper; you do not reuse the old jumpers.^[1]
5. In the app, pick the terminal labels that actually have wires. If the old thermostat has two label sets (conventional vs heat pump), use the set that matches the equipment.^[11]
6. Label each wire with the supplied stickers, one wire at a time, then remove the old base. Wrap the bundle around a pencil so nothing falls into the wall.^[1]

• Sensi Smart (ST55) and Sensi Lite: a C-wire is required for heat-only, cool-only, and heat-pump systems. Most conventional heat-and-cool systems can use power sharing without a C-wire. Apple HomeKit on the ST55 also requires a C-wire.^[3][4][12]
• Sensi Touch and Touch 2: a C-wire is required for all system types.^[3][9]
• Copeland's options if you do not have a C-wire: use a spare unused conductor landed on C at both ends; use the G (fan) wire as a C-wire as shown in their C-wire videos (the thermostat then manages the fan — explain this to the customer); or install a Common Wire Maker / add-a-wire kit. A 24 VAC transformer can also be added on a 2-wire heat-only system.^[3][5]

• Conventional furnace + AC: R (or RC/RH) to RC or RH, C to C, W to W/E, Y to Y, G to G, W2/Y2 if present. Leave the RC/RH jumper in place unless there are truly separate RC and RH wires.
• Heat pump: O or B to O/B, Y to Y (first-stage compressor heat and cool), AUX/E/W to W/E, C required, L if present. Outdoor equipment in the configuration menu must be HP1 or HP2, not AC1.^[6]

1. Level and screw the new base to the wall. Push each labeled wire into its terminal and tighten the screw. Tug-test every conductor.^[1]
2. Press the faceplate onto the base, restore power at the air handler and the breaker, and confirm the display comes up.

1. On the thermostat press Menu, then Mode. The Wi-Fi icon flashes and the display shows 00, 11, or 22 — that is the radio version.^[1]
2. Follow the app. After joining the Sensi network, enter the Sensi Security Code from the Welcome Guide or the back of the faceplate, then join the home 2.4 GHz network.^[1][2]
3. On iPhone/iPad, versions that show 11 or 22 can also be added to Apple HomeKit (C-wire required).^[1][4]

The app normally sets this from the wires you entered. To check or correct it at the thermostat:^[6][2]

• Menu → Next past °F/°C → Outdoor: AC1 or AC2 (conventional cooling), HP1 or HP2 (heat pump), AC0 if there is no Y wire.
• Indoor: GA1 or GA2 (gas / oil / boiler — the display may show 6A1/6A2), EL1 or EL2 (electric furnace), FAN if there is no W/E wire.
• Reversing valve: leave the default O. If the heat pump cools in Heat and heats in Cool, change it to B.^[6]

Humidifier / dehumidifier accessory settings are contractor options in the same menu (H AA, dH AA, set points).^[2]

• Models ST76 / 1F96U-42WF. A C-wire is required for every system type. There are no backup batteries; a blank screen usually means no 20–30 VAC between RH/RC and C.^[9][3]
• Wi-Fi setup is Menu → Wi-Fi, then scan the QR code on the Touch 2 screen (Bluetooth). Or enter the on-screen PIN. Still 2.4 GHz only.^[9]
• Extra ACC+ / ACC− (or ACCP) terminals and a dip switch support a whole-home humidifier. Clip the RC/RH jumper only on a two-transformer system, same idea as the ST55.^[10]
• Configuration path: Menu → Advanced Set Up → Set Up HVAC Equipment → Configure, with the same AC/HP and GA/EL/FAN and O/B choices.^[6]

• No display / no power (especially Touch / Touch 2): confirm breakers and door switches, tug-test C and R at the thermostat and at the control board, and measure 20–30 VAC between RH (or RC) and C. Less than 20 VAC will not run a Touch model.^[9]
• Wi-Fi drops or the Wi-Fi icon disappears (ST55): replace AA batteries if the battery icon is low (the radio shuts down to save batteries). On heat-only, cool-only, or heat-pump systems without a C-wire, Wi-Fi can drop after about two hours — that is a C-wire / compatibility issue, not a bad radio. Sensi is not designed to run on batteries alone.^[8][5]
• Heat and cool reversed on a heat pump: change the reversing-valve setting from O to B (or back).^[6]
• Short cycling or the wrong stage running: re-check outdoor/indoor configuration (AC vs HP, 1 vs 2 stage) and that Y2/W2 are on the correct terminals.
• E5 or ES — Call for Service: Copeland documents this as an internal power-supply protector that has tripped (surge or miswiring). Contact Sensi Technical Support. A temporary workaround they describe is to move the C-wire off C (power off first) so the thermostat can still run locally without Wi-Fi — this is a stopgap, not a repair.^[7]

1. Sensi — How to install Sensi smart thermostat (ST55 / 1F87U-42WF) — https://sensi.copeland.com/en-us/support/installation/installing-sensi-smart-thermostat
2. Sensi Smart Thermostat Manual Operation Guide, R-5029 (Nov 2024, models 1F87U-42WF, ST55) — https://media.copeland.com/bfc1e5ef-5156-4617-b9ae-b16b0105589b/R-5029%20-%20Sensi%20Smart%20Thermostat%20Manual%20Operation.pdf
3. Sensi — Do I need a c-wire? — https://sensi.copeland.com/en-us/support/c-wire
4. Sensi — System compatibility chart — https://sensi.copeland.com/en-us/support/compatibility
5. Sensi — Will Sensi thermostats work with my HVAC system? — https://sensi.copeland.com/en-us/support/how-can-i-be-sure-a-sensi-thermostat-will-work-with-my-hvac
6. Sensi — How do I configure my thermostat? — https://sensi.copeland.com/en-us/support/how-do-i-configure-my-thermostat
7. Sensi — E5 (ES) Call for Service — https://sensi.copeland.com/en-us/support/e5-thermostat-error
8. Sensi — No Wi-Fi icon on thermostat — https://sensi.copeland.com/en-us/support/no-wi-fi-icon-on-my-thermostat
9. Sensi — How to install Sensi Touch 2 — https://sensi.copeland.com/en-us/support/installation/installing-sensi-touch2-smart-thermostat
10. Sensi — Thermostat comparison (terminals and C-wire) — https://sensi.copeland.com/en-us/products/sensi-thermostat-comparison
11. Sensi — What terminal should I select in the Sensi app? — https://sensi.copeland.com/en-us/support/terminal-to-select-in-sensi-app
12. Sensi — Does my Sensi thermostat need a common wire? — https://sensi.copeland.com/en-us/support/does-my-sensi-thermostat-need-a-common-wire-or-c-wire