1. Terminals the T5+ takes
Honeywell’s T5+ Smart Thermostat product data (document 33-00474) has a wire-recording table with the terminals below. Wires on any terminal that is not on this list need extra support, so check with Honeywell support before going further.
| Terminal | Job on the T5+ |
|---|---|
| R, Rh, Rc | 24 VAC power from the system transformer. See the R-switch section below. |
| C | 24 VAC common. The manual marks it required. |
| W, W2 or AUX | Heat call, or second-stage and auxiliary heat. |
| Y, Y2 | Cooling call, first and second stage. |
| G | Fan. |
| O/B | Reversing valve on a heat pump. Set the energize mode in ISU 218. |
| E | Emergency heat on a heat pump. |
| A or L/A, K | Listed on the manual’s worksheet. Look up their use in the manual before you connect wires to them. |
The manual says S and U terminals are not supported. The S terminals are for indoor and outdoor sensors, and the U terminals are for a ventilation relay.
2. Setting the R-switch
The R-switch is on the wall plate (UWP) and has to match your wiring before you push the wires in. Honeywell’s steps are:
- One R-type wire (R, Rh or Rc): set the R-switch to the up position, then insert that wire into the R terminal.
- Two R-type wires (R or Rh, plus Rc): set the R-switch to the down position, insert the Rc wire into the Rc terminal, and insert the R or Rh wire into the R terminal.
Two R wires usually mean two separate transformers, one for heating and one for cooling. That setup is covered in the two-transformer wiring guide, and the difference between the terminals is explained on the Rh and Rc page.
3. Jumpers and counting wires
Before you disconnect the old thermostat, photograph the wall plate, with the letters next to each terminal visible. Then write down each wire’s terminal and color. The manual says to leave jumpers out of that count. A jumper is a small metal staple or a short colored wire that links one terminal to another, and it must be removed. It says the T5+ does not need one, so do not reconnect it.
If the old wall plate has faded colors or two wires share the same color, use the wire labels in the box to mark each one before you disconnect it. Our wire color guide explains why colors alone can’t be trusted.
4. No C wire
The manual lists a C wire as required for the T5+. Work through these options in order:
- Look for an unused wire. The manual says an extra wire may be pushed into the wall or wrapped around the bundle. Pull the bundle gently out of the wall to check. If you find one, connect it to C at the thermostat and to the C terminal on the heating and cooling equipment, or on the zone panel in a multi-zone home.
- Use the C-Wire Power Adapter. If there is no spare wire and the system uses Y and G, Honeywell’s THP9045A C-Wire Power Adapter can supply the power. The product data lists it as an option for this case.
- Check the system manual. The manual notes that not all equipment labels its 24 VAC common as C. If the equipment has no C terminal, find out from its manual or the manufacturer which terminal is the 24 VAC common.
Before you add an adapter or run a new wire, measure the 24 VAC circuit. The multimeter guide shows how.
5. Installing the wires, step by step
These steps follow Honeywell’s install sequence. Turn the power off at the breaker box or switch before you touch any wire.
- Turn the system off and remove the old thermostat. Do not disconnect any wires until you have photographed them.
- Check there are no 120 or 240 V wires. The manual says a thick black wire with a wire nut, or a thermostat that runs at 120 V, means a line-voltage system the T5+ won’t work with.
- Set the R-switch to match your R wires, as described in section 2.
- Release each wire from its old terminal with a small screwdriver. Wrap the wires around a pencil so they don’t fall back into the wall.
- Insert each wire into its own terminal on the wall plate, one wire per terminal, using the inner holes. Tug each wire to check it is secure. The manual says to strip 1/4 to 3/8 inch of copper.
- Mount the wall plate with the three supplied screws, then snap the thermostat on.
- Turn the power on at the breaker box or switch. Confirm the screen shows START SETUP, then continue with the Resideo app or manual setup.
6. Heat pump settings (ISU)
The T5+ uses ISU (installer setup) numbers. The manual lists these for heat pumps:
| ISU | Name | What to choose |
|---|---|---|
| 200 | System Type | Heat Pump |
| 218 | Reversing Valve | O/B on cool, or O/B on heat, to match the equipment |
| 220 | Cool Stages | 0, 1 or 2 |
| 221 | Heat Stages / Aux/E Stages | Heat stages 0, 1 or 2, and AUX/E stages 0 or 1 |
The manual says a heat pump can have at most one Aux/E stage. Choose the reversing valve mode from the equipment’s manual or the control board labels, not from the wire color. For a worked example with a different Honeywell model, see the Honeywell T6 Pro heat pump guide, and for what the O/B wire does, the O/B terminal page.
7. What the T5+ will not work with
- Line voltage: electric baseboard heat, or any system at 120 to 240 V.
- Millivolt systems, such as some older gas fireplaces and wall heaters.
- S and U terminals: indoor and outdoor sensors and ventilation relays are not supported.
If a wire is in a terminal you can’t identify, stop and check the equipment manual. For general fault steps once it is wired, see the thermostat troubleshooting checklist.
8. Frequently asked questions
What does the R-switch on a Honeywell T5+ do?
It tells the thermostat whether it has one R-type wire or two. With one wire (R, Rh or Rc), set the R-switch up and put that wire in the R terminal. With two wires, set the R-switch down, put the Rc wire in Rc and the R or Rh wire in R. Set it before you push the wires in, and match it to the labels you wrote down when you photographed the old wiring.
Does the Honeywell T5+ need a jumper between Rh and Rc?
No. Honeywell’s manual says the thermostat does not need jumpers and tells you to remove any jumper from the old wall plate before you connect new wires. A jumper is a small metal staple or a short colored wire that links one terminal to another. Leave it out of the wire count, too.
Can I install a Honeywell T5+ without a C wire?
Sometimes. The manual lists a C wire as required, so first look for an unused wire in the wall bundle and connect it to C at both ends. If there is none and the system uses Y and G, Honeywell offers the THP9045A C-Wire Power Adapter. Otherwise you need a new run of wire. See the no C wire guide for the other options.
Which ISU settings should a Honeywell T5+ heat pump use?
Set ISU 200 to Heat Pump, then check ISU 218, which chooses whether the O/B reversing valve energizes on cool or on heat. The manual lists ISU 220 for cool stages and ISU 221 for heat stages and Aux/E stages. A heat pump can have at most one Aux/E stage. Match the reversing valve setting to your equipment’s manual, because the two conventions differ between brands.
Will a Honeywell T5+ work on 120 V baseboard heat or a millivolt system?
No. The manual says it does not work with electric baseboard heat (120 to 240 V) or with millivolt systems. Those are line-voltage or different low-voltage systems. It also does not support S terminals for indoor and outdoor sensors, or U terminals for ventilation relays.