PRO Digital Thermostat TH3110D

Honeywell PRO TH3110D Thermostat

The Honeywell PRO TH3110D is a non-programmable digital thermostat designed to control single-stage heating and cooling systems. It provides electronic control for compatible 24 VAC HVAC equipment and 750 mV heating systems.

The thermostat features a digital temperature display, up and down temperature buttons, a System switch with Heat, Off, and Cool positions, and a Fan switch with Auto and On settings. It can operate using two AA alkaline batteries, a 24 VAC common-wire connection, or a common wire with battery backup.

Installation involves mounting the wallplate, connecting the appropriate thermostat terminals, selecting the correct fan operation setting, installing batteries if required, and configuring the thermostat for the connected heating or cooling equipment.

Important: The Honeywell TH3110D must be installed by a trained, experienced technician. Electrical power must be disconnected before installation or wiring work begins.

Product Overview

The Honeywell PRO TH3110D provides temperature control for compatible residential heating and cooling equipment.

It uses a digital screen to display the current indoor temperature, selected temperature, system operation, and low-battery warnings.

Main Features

• Non-programmable operation: Provides direct temperature adjustment using dedicated buttons.
• Single-stage HVAC control: Supports one stage of heating and one stage of cooling.
• Digital temperature display: Shows the current indoor temperature and selected setting.
• Heating and cooling control: Includes Heat, Off, and Cool system positions.
• Fan control: Provides Auto and On settings.
• Multiple power options: Supports battery power, common-wire power, or common-wire power with battery backup.
• Installer configuration: Allows settings to match the connected HVAC system.
• Adjustable cycle rates: Provides heating and compressor cycle-rate configuration.
• Temperature units: Supports Fahrenheit and Celsius.
• Compressor protection: Delays compressor restarting to reduce equipment damage.
• Low-battery indication: Displays a Replace Batt warning when battery replacement is required.
• Installer system test: Supports verification of heating, cooling, and thermostat information.

Compatible Heating and Cooling Systems

The Honeywell TH3110D supports several heating and cooling configurations.

The thermostat is designed for single-stage heating and cooling control.

It must be configured according to the connected equipment before the installation is considered complete.

Technical Specifications

What’s Included in the Box

The Honeywell PRO TH3110D package contains the thermostat, installation hardware, batteries, and operating instructions.

Required Installation Tools

The following tools and supplies are required for installation.

Parts and Components

The Honeywell TH3110D consists of a digital display, temperature adjustment buttons, System and Fan switches, a removable thermostat body, and a wallplate with wiring terminals.

Thermostat Controls and Display

The thermostat has two temperature adjustment buttons and two mechanical switches.

Temperature Adjustment Buttons

The Up and Down buttons are positioned on the right side of the thermostat.

• Up: Increases the selected temperature.
• Down: Decreases the selected temperature.

The thermostat display shows the selected temperature while adjustments are made.

System Switch

The System switch determines whether the thermostat controls heating, cooling, or neither.

Fan Switch

The Fan switch determines whether the connected system fan runs continuously or operates during heating or cooling.

Display Indicators

Important Safety Instructions

The Honeywell PRO TH3110D controls electrical heating and cooling equipment. Incorrect installation or wiring may damage the thermostat, connected HVAC equipment, or create a hazardous electrical condition.

Installation Safety

• Installation must be performed by a trained, experienced technician.
• Read the installation instructions before beginning work.
• Verify that the thermostat is compatible with the connected equipment.
• Check the electrical ratings before making connections.
• Disconnect electrical power before installation.
• Do not work on energized thermostat wiring.
• Use the recommended thermostat wire size.
• Follow the wiring configuration appropriate to the heating or cooling equipment.
• Confirm that all terminal screws are secure.
• Complete the installer setup before testing the system.
• Always test heating and cooling operation after installation.

Electrical Hazard Warning

Caution: Electrical hazard.

Electrical power must be disconnected before removing, installing, or wiring the thermostat.

Failure to disconnect power may cause electrical shock or equipment damage.

Equipment Damage Warning

The compressor protection delay is bypassed during the installer system test.

Caution: Avoid cycling the compressor quickly during testing. Rapid compressor cycling may damage the connected equipment.

Mercury Disposal Notice

If the Honeywell TH3110D replaces an older thermostat containing mercury in a sealed tube, the old thermostat must not be discarded with ordinary household trash.

Contact the local waste management authority for instructions about recycling and proper disposal.

Before Installation

Before installing the Honeywell TH3110D, the technician must confirm the installation location, electrical compatibility, wiring requirements, and included components.

Pre-Installation Checklist

1. Confirm that the thermostat and supplied mounting hardware are present.
2. Identify the type of heating and cooling system.
3. Verify that the system is compatible with the thermostat’s electrical ratings.
4. Identify the existing thermostat wiring.
5. Disconnect electrical power to the heating and cooling equipment.
6. Select an appropriate wall location.
7. Prepare the required installation tools.
8. Determine whether battery power, common-wire power, or both will be used.

Choosing the Thermostat Installation Location

The thermostat should be mounted where it can measure the average indoor temperature accurately.

Recommended Mounting Height

Install the thermostat approximately 5 feet (1.5 meters) above the floor.

The location should have good air circulation and represent the average temperature of the room.

Locations to Avoid

Do not install the thermostat where temperature measurements may be affected by:

• Drafts or areas with little air movement behind doors.
• Corners and other dead-air spaces.
• Hot or cold air from ventilation ducts.
• Direct sunlight.
• Radiant heat from appliances.
• Concealed pipes.
• Chimneys.
• Unheated or uncooled areas behind the wall.
• Exterior walls that may affect the thermostat temperature reading.

A suitable installation position helps the thermostat respond to the actual indoor temperature rather than localized heating or cooling.

Wallplate Installation Instructions

The Honeywell PRO TH3110D wallplate is attached to the back of the thermostat before installation.

It must be removed and mounted to the wall before wiring.

Step 1: Remove the Wallplate

1. Disconnect power to the HVAC system.
2. Hold the thermostat securely.
3. Grasp the top and bottom of the wallplate.
4. Pull the wallplate away from the thermostat body.

Step 2: Position the Wallplate

1. Pull the thermostat wires through the wallplate’s central wire opening.
2. Place the wallplate against the selected wall location.
3. Align the wallplate.
4. Use a level if necessary.
5. Mark the mounting hole positions with a pencil.

Step 3: Drill the Mounting Holes

Use the drill bit size appropriate for the wall material.

1. 
   Drill the holes at the marked positions.
2. Insert the supplied wall anchors.
3. Tap the anchors into place using a hammer.

Step 4: Secure the Wallplate

1. Position the wallplate over the installed anchors.
2. Align the mounting holes.
3. Insert the supplied mounting screws.
4. Tighten the screws securely.

The wallplate is now ready for the wiring connections.

Honeywell TH3110D Wiring Instructions

The Honeywell TH3110D uses a terminal block to connect to compatible heating, cooling, fan, and transformer circuits.

Warning: Wiring must be performed by a trained, experienced technician with power disconnected.

Thermostat Terminal Designations

R and Rc Terminal Functions

The Rc terminal connects to the secondary side of the cooling system transformer.

The R terminal connects to the secondary side of the heating system transformer.

C Terminal Function

The C terminal connects to the common side of the cooling system transformer.

This connection is optional when the thermostat is powered by batteries.

How to Connect the Thermostat Wiring

The technician must follow the wiring configuration appropriate to the installed HVAC system.

General Wiring Procedure

1. Confirm that electrical power is disconnected.
2. Identify the correct thermostat terminal connections.
3. Loosen the appropriate terminal screws.
4. Insert the thermostat wires into the terminal block.
5. Tighten the terminal screws securely.
6. Push excess wire back into the wall opening.
7. Keep the wires within the designated wiring area.
8. Plug the wall opening with nonflammable insulation.

The insulation helps prevent drafts from entering the thermostat and affecting temperature sensing.

Recommended Thermostat Wire

Use 18- to 22-gauge thermostat wire.

Shielded cable is not required.

R and Rc Jumper Settings

The thermostat includes a factory-installed metal jumper between the R and Rc terminals.

The jumper configuration depends on the number of transformers in the system.

Important: Remove the R/Rc jumper for two-transformer systems only.

Incorrect jumper configuration may affect heating or cooling operation.

Heat Pump Wiring Requirements

When installing the TH3110D with a compatible heat pump, additional wiring and setup requirements apply.

Heat Pump Jumper

For heat pump installations, a short piece of wire must connect the W and Y terminals.

This jumper wire is not included with the thermostat.

Heat Pump Changeover Valve

The thermostat provides two terminals for the heat pump changeover valve.

Use the O or B terminal according to the connected heat pump configuration.

Heat Pump Fan Setting

For a heat pump system:

1. Set the internal Fan Operation Switch to Electric/Heat Pump.
2. Configure the thermostat for a heat pump using Installer Setup Function 1.

The system type and fan configuration must match the installed equipment.

Supported Wiring Configurations

The installation guide provides wiring diagrams for the following configurations.

Wiring Diagram Notes

• Provide appropriate electrical disconnects and overload protection.
• Remove the factory R/Rc jumper only for two-transformer systems.
• Use either O or B for the heat pump changeover valve.
• Install the W-to-Y jumper for heat pump wiring.
• Select the Electric/Heat Pump fan setting for heat pump systems.
• Use the C terminal when a 24 VAC common-wire connection is required.

All connections must match the actual HVAC equipment and the appropriate system wiring diagram.

Fan Operation Switch Settings

The thermostat has an internal Fan Operation Switch.

This switch determines how the thermostat controls the heating system fan.

Gas or Oil Heating

For gas or oil heating systems:

• Leave the Fan Operation Switch in the factory-set Gas or Oil position.
• This setting is intended for heating systems that control the fan during a call for heat.

Electric Heating or Heat Pump

For electric heating or heat pump systems:

1. Locate the internal Fan Operation Switch.
2. Move it to Electric or Heat Pump.
3. Complete the corresponding installer configuration.

This setting allows the thermostat to control the fan during a call for heat when a fan wire is connected to the G terminal.

Fan Operation Comparison

Power Options and Battery Installation

The Honeywell TH3110D supports battery power and 24 VAC common-wire power.

Available Power Methods

AC Power Connection

For AC power:

1. Connect the common side of the cooling system transformer to the C terminal.
2. Follow the appropriate transformer configuration.
3. Retain or remove the R/Rc jumper according to the number of transformers.

The R/Rc jumper must only be removed in two-transformer systems.

How to Install the AA Batteries

The battery compartment is located on the back of the thermostat body.

1. Access the rear battery compartment.
2. Locate the battery positions.
3. Insert two AA alkaline batteries.
4. Match the positive (+) and negative (−) ends to the marked polarity.
5. Check that the batteries are seated correctly.

Battery installation is optional when the thermostat receives AC power.

When batteries are installed alongside AC power, they can provide backup power to the display during an electrical power interruption.

Mounting the Thermostat

After the wallplate has been installed and the wiring completed, the thermostat body can be attached.

How to Attach the Thermostat to the Wallplate

1. Locate the four mounting tabs on the wallplate.
2. Align the tabs with the matching slots on the thermostat body.
3. Position the thermostat against the wallplate.
4. Push gently until the thermostat snaps into place.

Make sure the thermostat is secured before restoring power and testing operation.

Installer Setup Instructions

The Installer Setup menu allows the technician to configure the thermostat for the connected heating and cooling equipment.

Settings include system type, heating cycle rate, compressor cycle rate, temperature units, and compressor protection.

How to Enter Installer Setup

1. Locate the Up and Down temperature buttons.
2. Press and hold both buttons simultaneously.
3. Continue holding until the display changes to the setup screen.

The setup display shows:

• Function number.
• Selected setting.

Installer Setup Button Functions

Installer Setup Function 1: System Type

Function 1 determines the type of heating and cooling equipment connected to the thermostat.

When Heat Pump is selected, a 5-minute compressor off time applies to heating and cooling.

Installer Setup Function 5: Heating Cycle Rate

Function 5 controls the heating cycle rate.

CPH means cycles per hour.

Heating Cycle Rate Settings

Additional selectable cycle-rate values include:

2, 4, 6, 7, 8, 10, 11, and 12 CPH.

The heating cycle-rate setting must match the connected equipment.

Installer Setup Function 9: Compressor Cycle Rate

Function 9 controls the compressor cycle rate.

Other available settings are:

1, 2, 4, 5, and 6 CPH.

The compressor setting should be selected according to the equipment requirements.

Installer Setup Function 14: Temperature Display

Function 14 selects the temperature unit displayed by the thermostat.

How to Change Fahrenheit to Celsius

1. Enter Installer Setup.
2. Advance to Function 14.
3. Change the setting from 0 to 1.
4. Save the configuration.

Setting 0 displays temperature in Fahrenheit.

Setting 1 displays temperature in Celsius.

Installer Setup Function 15: Compressor Protection

Function 15 controls the compressor minimum off time.

This setting helps prevent equipment damage caused by restarting the compressor too soon after shutdown.

Compressor Protection Settings

The guide identifies 5 minutes as the recommended compressor protection setting.

How Compressor Protection Works

When the cooling system stops, the thermostat may prevent the compressor from restarting immediately.

During the waiting period:

• Cool On flashes on the display.
• Heat On may flash when operating a heat pump.
• The compressor remains off during the protection delay.

When the required waiting time has elapsed, the indicator stops flashing and the compressor is allowed to start.

This is a normal protection function.

Installer System Test

The thermostat includes an installer testing function for checking heating and cooling operation.

Important: System testing must be performed by a trained technician.

How to Enter System Test

After completing Installer Setup, press the Up temperature button again to enter the Installer System Test.

The screen displays the system test number and current status.

Testing the Cooling System

1. Set the System switch to Cool.
2. Select the cooling system’s On test status.
3. Verify that the compressor and fan operate.
4. Return the cooling test status to Off.

Testing the Heating System

1. Set the System switch to Heat.
2. Select the heating system’s On test status.
3. Verify that the heating equipment operates.
4. Return the heating test status to Off.

System Test Status Codes

When the Fan Operation Switch is set to Electric Heat/Heat Pump, the fan turns on immediately during a heating test.

Thermostat Information Test

With the System switch set to Off, the installer can view thermostat information using Test 70.

This information is provided for reference.

Exiting System Test

Press and hold both temperature buttons to terminate the system test.

Compressor Testing Warning

Caution: Equipment damage hazard.

The compressor protection delay is bypassed during installer testing.

Avoid switching the compressor on and off rapidly during tests.

Operating Instructions

After installation and system testing, the thermostat can be used to control the connected heating or cooling system.

How to Set the Heating Temperature

1. Move the System switch to Heat.
2. Press the Up or Down button.
3. Select the desired heating temperature.
4. The thermostat will control the heating system according to the selected setting.

Available heating temperature range:

40°F–90°F (4.5°C–32°C).

How to Set the Cooling Temperature

1. Move the System switch to Cool.
2. Press the Up or Down button.
3. Select the desired cooling temperature.
4. The thermostat will control the cooling system according to the selected setting.

Available cooling temperature range:

50°F–99°F (10°C–37°C).

How to Turn Heating and Cooling Off

Move the System switch to Off.

The thermostat will stop calling for heating or cooling.

How to Run the Fan Continuously

Move the Fan switch to On.

The fan will run continuously.

How to Use Automatic Fan Operation

Move the Fan switch to Auto.

The fan will operate when the heating or cooling system is running, according to the installed equipment configuration.

Compressor Protection and System Status

The thermostat displays messages that indicate heating and cooling activity.

Heat On Indicator

Heat On appears when the thermostat calls for heating.

If Heat On does not appear:

1. Set the System switch to Heat.
2. Select a temperature higher than the current room temperature.

Cool On Indicator

Cool On appears when the thermostat calls for cooling.

If Cool On does not appear:

1. Set the System switch to Cool.
2. Select a temperature lower than the current room temperature.

Flashing Heat On or Cool On

A flashing Heat On or Cool On message may indicate that the compressor protection delay is active.

Wait for the required restart interval.

The guide recommends a 5-minute compressor protection setting.

Battery Replacement

The thermostat displays Replace Batt when battery replacement is required.

How to Replace the Batteries

1. Access the rear battery compartment.
2. Remove the used batteries.
3. Insert two fresh AA alkaline batteries.
4. Follow the polarity markings.
5. Reinstall the thermostat body correctly.

When AC power is used with battery backup, the batteries can maintain display power during interruptions.

Troubleshooting Guide

The following troubleshooting procedures address blank displays, temperature adjustment problems, heating and cooling failures, fan operation, and compressor protection messages.

Honeywell TH3110D Display Is Blank

If the thermostat screen is blank:

1. Check the circuit breaker.
2. Reset the breaker if necessary.
3. Confirm that the heating and cooling equipment power switches are on.
4. Check that the equipment door is securely closed.
5. If using battery power, confirm that fresh AA alkaline batteries are installed correctly.

Honeywell TH3110D Temperature Cannot Be Changed

The thermostat allows temperature adjustments within specific limits.

Make sure the selected setting is within the permitted range.

Honeywell TH3110D Heat Not Working

If Heat On appears but the heating equipment does not respond, the guide specifies electrical and wiring checks for a qualified technician.

These include:

1. Checking for 24 VAC at the secondary side of the equipment transformer between power and common.
2. Checking for 24 VAC between the W terminal and transformer common.
3. Inspecting the heating equipment if the expected voltage is absent.
4. Checking for loose or broken wiring between the thermostat and heating equipment.

If 24 VAC is present between the W terminal and transformer common during the test, the thermostat is functioning and the heating equipment should be checked for the cause.

Warning: These checks involve electrical circuits and must be performed by a trained technician.

Honeywell TH3110D Cooling Not Working

If Cool On appears but the air conditioning system does not operate, a qualified technician should check:

1. The equipment’s 24 VAC power supply.
2. The voltage between the Y terminal and transformer common.
3. The cooling equipment.
4. Loose or broken connections between the thermostat and cooling equipment.

If 24 VAC is present between Y and transformer common during the test, the thermostat is functioning and the cooling system should be inspected.

Honeywell TH3110D Fan Not Turning On

If the fan does not turn on during a call for heat:

1. Check the connected heating system type.
2. Verify the internal Fan Operation Switch setting.
3. Confirm that the setting matches Gas/Oil or Electric/Heat Pump operation as applicable.

The internal switch should only be adjusted by the installer or a qualified technician.

Honeywell TH3110D Cool On Flashing

When Cool On flashes, the compressor protection delay is active.

Wait approximately 5 minutes for the compressor to restart safely when the recommended protection setting is used.

Do not repeatedly force the system to restart.

Honeywell TH3110D Heat On Flashing

On a heat pump installation, Heat On may flash while compressor protection is active.

The message stops flashing when the safe restart interval has elapsed.

Heat On or Cool On Does Not Appear

If Heat On is not displayed:

• Set the System switch to Heat.
• Select a temperature higher than the current indoor temperature.

If Cool On is not displayed:

• Set the System switch to Cool.
• Select a temperature lower than the current indoor temperature.

Replacement Parts and Accessories

The installation guide identifies a cover plate assembly that can be ordered separately.

Contact a Honeywell distributor to order the listed accessory.

Customer Support Information

The Honeywell PRO TH3110D installation guide identifies the following manufacturer and company contact details.

For installation-related equipment compatibility, wiring, or control problems, a trained HVAC technician should inspect the installation and connected system.

Frequently Asked Questions

How do I install the Honeywell TH3110D thermostat?

The Honeywell TH3110D must be installed by a trained, experienced technician. Installation involves disconnecting electrical power, mounting the wallplate approximately 5 feet above the floor, connecting the appropriate thermostat terminals, configuring the fan setting, installing batteries or connecting common-wire power, mounting the thermostat body, and completing the installer setup and system tests.

What batteries does the Honeywell PRO TH3110D use?

The Honeywell PRO TH3110D uses two AA alkaline batteries. The batteries can provide primary power or backup power for the display when a 24 VAC common-wire connection is used.

What are the Honeywell TH3110D wiring terminals?

The thermostat has W, Y, G, O, Rc, R, B, and C terminals. They provide connections for the heating relay, compressor contactor, fan relay, heat pump changeover valve, heating and cooling transformer power, and common wire. Wiring must match the HVAC equipment and be completed by a qualified technician.

How do I change the Honeywell TH3110D from Fahrenheit to Celsius?

Enter Installer Setup by pressing and holding both temperature buttons. Advance to Function 14 and change its value to 1 for Celsius. Setting 0 selects Fahrenheit. Press and hold the Up button to save and exit.

Why is Cool On flashing on my Honeywell TH3110D thermostat?

A flashing Cool On message indicates that compressor protection is preventing an immediate restart. The recommended delay is 5 minutes. When the waiting period ends, the message stops flashing and the compressor can restart.

Why is the Honeywell TH3110D display blank?

A blank display may be caused by a tripped circuit breaker, an equipment power switch being off, an open equipment door, or depleted AA batteries. Check these conditions and replace the batteries when necessary.

How do I set the fan on my Honeywell TH3110D thermostat?

Use the Fan switch on the front of the thermostat. Select On to run the fan continuously or Auto to operate the fan when the heating or cooling system is running. The internal Fan Operation Switch must also be configured correctly for the type of heating equipment.

What is the Honeywell TH3110D temperature range?

The thermostat supports heating settings from 40°F to 90°F (4.5°C to 32°C) and cooling settings from 50°F to 99°F (10°C to 37°C). The temperature unit can be changed between Fahrenheit and Celsius using Installer Setup Function 14.