Honeywell T6861 Series Large LCD Digital Thermostat
110/220 VAC | 2-pipe/4-pipe fan coil control
Application
T6861 digital thermostats are designed for application of 3-speed fan and valves in fan coil systems. They support:
- 2-pipe cool only/heat only/manual changeover and 4-pipe manual or automatic changeover
- Ventilation mode
- Manual or automatic 3-speed fan control
- Water valve control
Fan speed can be selected for automatic or manual 3-speed control. In ventilation mode, the fan only supports manual speed control.
Features
- Super modern appearance design, suitable for office, hotel, and residential buildings.
- Horizontal and vertical models available for varied applications.
- Slim design, direct installation on 86-size boxes.
- Stylish and elegant blue/green backlight with blue/green color ring.
- 2-pipe/4-pipe integrated into one unit with easy configuration.
- Big LCD display with English and icons.
- Easy to install and set-up.
- Time on/off function.
- Selectable room temperature or setpoint display.
- Manual or automatic fan speed selection.
- Remote temperature sensor support.
- Energy saving mode activation by button press or dry contact (key card).
- Cycle per Hour (CPH) function.
- Adjustment of display room temperature.
- Temperature unit selectable (°C or °F).
- User settings are retained when power is off.
- Freezing protection function available.
- Lock or unlock keys or parts of keys in Installer Set-up.
- Heat and cool setpoint limitation for energy saving.
Model Summary
| Model | Horizontal/Vertical | Backlight | Color Ring | Time on/off | 2-pipe/4-pipe | Power supply (V) | Energy Saving | Ventilation | Manual/Automatic Fan | Remote Sensor |
|---|---|---|---|---|---|---|---|---|---|---|
| T6861H2BB T6861H2WB | Horizontal | Blue | Blue/White | Y | 2/4 | 220 | Y | Y | Y | Y |
| T6861V2BB T6861V2WB | Vertical | Blue | Blue/White | Y | 2/4 | 220 | Y | Y | Y | Y |
| T6861H2GG T6861H2WG | Horizontal | Green | Green/White | Y | 2/4 | 220 | Y | Y | Y | Y |
| T6861V2GG T6861V2WG | Vertical | Green | Green/White | Y | 2/4 | 220 | Y | Y | Y | Y |
| T6861H1BB T6861H1WB | Horizontal | Blue | Blue/White | Y | 2/4 | 110 | Y | Y | Y | Y |
| T6861V1BB T6861V1WB | Vertical | Blue | Blue/White | Y | 2/4 | 110 | Y | Y | Y | Y |
| T6861H1GG T6861H1WG | Horizontal | Green | Green/White | Y | 2/4 | 110 | Y | Y | Y | Y |
| T6861V1GG T6861V1WG | Vertical | Green | Green/White | Y | 2/4 | 110 | Y | Y | Y | Y |
Note: Horizontal models are shown as samples for display.
Mechanical Design
Thermostat Appearance
Images of the T6861 thermostat in horizontal and vertical orientations, displaying various settings and icons.
The thermostat features a digital display, and buttons for FAN, POWER, MODE, UP, and DOWN control.
LCD Display Indicators
The LCD display provides various indicators:
- Room Temperature
- Current Fan Setting (Low, Med, High, Auto)
- Thermostat Status (Off, Heat On, Cool On)
- Current Mode Setting
- Time on/off setting indicator
- Keypad lock status (entirely or partly locked)
- Setpoint
- Installer Setup indicator
- Heat/Cool Setpoint
- Installer Test indicator
- Length of Time on/off
- Thermostat "calling" for heat or cool
- Occupied/Unoccupied status
- Freezing Protection Mode indicator
Function
Valve Control
The thermostat maintains the setpoint by controlling the on/off valve based on acquired room temperature (from integrated or external sensor).
Fan Operation
Fan speed can be set to manual or automatic 3-speed operation. In manual mode, fan speed is set via control outputs (Gh, Gm, Gl). In automatic mode, fan speed adjusts based on the difference between room temperature and setpoint. When room temperature reaches setpoint, the valve closes, and the fan also stops.
A graph illustrates fan speed control based on the difference between room temperature and setpoint, showing fan speed ramping from off to high or vice versa in heating and cooling modes.
Four-Pipe Application
For 4-pipe systems with Automatic Change Over (ACO), a fixed deadband is set in the Installer Setup (ISU). The heating and cooling setpoints define this deadband.
If the difference between heating and cooling setpoints is less than the enforced deadband, the ISU deadband is applied. Adjusting one setpoint may automatically adjust the other to maintain the deadband (e.g., heating setpoint = cooling setpoint - deadband). Heating and Cooling range stops define the maximum heating and minimum cooling setpoints.
A diagram illustrates the concept of deadband and setpoints for 4-pipe auto changeover systems, showing heating and cooling setpoints relative to the deadband.
The last system control mode used determines the mode in ACO when within the deadband.
Temperature Display
The displayed temperature can be set to show either the acquired room temperature or the setpoint. Both can be displayed simultaneously. This setting is configured during the Installer Set-Up process.
Cycle Per Hour (CPH)
The CPH function helps achieve more accurate temperature control by allowing the thermostat to open the valve multiple times per hour, even when the temperature is close to the setpoint (within ½ P-band). Default values are 4 for heating and 3 for cooling, adjustable in Installer Set-Up.
Time On/Off
The thermostat can be set to turn on or off automatically. Holding the power button for 3 seconds switches between time-on and time-off modes. The setting range is 0 to 12 hours, with 0.5-hour increments. The default time is 0.
An indicator shows when the thermostat has been set to Time Off.
Backlight
Any key press activates the backlight, which times out after 8 seconds of inactivity. In Installer Set-up and Installer Test modes, the backlight times out after 60 seconds.
Remote Temperature Sensor
The T6861 can control based on either the room's ambient temperature or the return air temperature using a remote temperature sensor (model NTC20K).
Keypad Lock
Keypad lock functionality can be configured in Installer Set-Up (ISU). Options include locking out the Mode button, Fan and Mode buttons, or all buttons. The default setting allows all keys to be available.
Operating Modes
Comfort Mode
In Comfort mode, the setpoint can be adjusted using the UP/DOWN buttons. This mode supports cool only, heat only, and manual heat/cool changeover applications.
Images of the thermostat display showing temperature setting adjustments.
Ventilation Mode
Pressing the MODE button enters Ventilation mode. In this mode, the valve output is inactive, and the fan operates based on the selected fan speed.
Energy Saving Mode
Energy Saving mode can be activated via a potential-free dry contact (like a hotel key card) or by pressing the MODE button continuously for 3 seconds. An energy saving icon appears on the screen.
The dry contact can be configured as normally open or normally closed in ISU. If activated by dry contact, all buttons are locked except for ISU multi-key functions. If activated by button press, subsequent button presses will stop energy saving mode.
For heating, the setpoint changes to a remote setback heating setpoint (10°C to 21°C, default 18°C). For cooling, it changes to a remote setback cooling setpoint (22°C to 32°C, default 26°C). These values can be adjusted in ISU in 0.5°C increments.
Freezing Protection Mode
Freezing protection can be disabled (default) or enabled. When enabled and the thermostat is in OFF mode, if the acquired temperature drops below 6°C, the thermostat will activate heat mode until the temperature reaches 8°C or the thermostat is turned on. This mode is not applicable to cool-only applications.
Images of the thermostat display showing 'Freezing Protection' mode and 'On/Off' mode indicators.
On/Off Mode
Pressing the power button switches the thermostat between on and off modes.
Technical Specification
- Power Supply: 110 (+/-10%) VAC, 220(+10%, -15%) VAC
- Frequency: 50/60Hz
- Control Algorithm: PI, On/off output
- Accuracy: +/-1°C at 21°C
- Rating Capacity: For 220V: 4(2)A for fan load, 2(1)A for zone valve. For 110V: 4(2)A for fan load, 2(1)A for zone valve.
- Cycle Times: 100,000 times
- Setpoint Range: 10~32°C
- Display Range: 0~37°C
- Installation: Mounted on 86x86mm junction box or US2x4 inch.
- Protection Class: IP20
- Environmental Conditions: Operation temperature -18~49°C, Shipping temperature -35~65°C, Relative humidity 5~90%.
Terminal Designations
| Item | Terminal | Description |
|---|---|---|
| 1 | Cc | Cooling close |
| 2 | Y | Cooling open |
| 3 | L | AC Power |
| 4 | Ch/Cc | Heating close/Cooling close |
| 5 | W/Y | Heating open/Cooling open |
| 6 | N | AC Ground |
| 7 | Gh | High speed fan relay |
| 8 | Gm | Medium speed fan relay |
| 9 | Gl | Low speed fan relay |
| 10 | Sc | Ground for remote sensor and remote setback |
| 11 | RSB | Remote set back |
| 12 | Rs | Remote sensor |
Wiring Diagrams
Detailed wiring diagrams are provided for various applications:
Application 1: 2 pipes heat only wiring diagram
Diagram showing connections for a 2-pipe heat-only system, including terminals for heat valve, fan, remote setback, and remote sensor.
Typical wiring for ON/OFF control in 2 pipe heating only (VC4013)
Typical wiring for ON/OFF control in 2 pipe heating only (VC6013)
Application 2: 2 pipes Cool only wiring diagram
Diagram showing connections for a 2-pipe cool-only system, including terminals for cool valve, fan, remote setback, and remote sensor.
Typical wiring for ON/OFF control in 2 pipe cooling only (VC4013)
Typical wiring for ON/OFF control in 2 pipe cooling only (VC6013)
Application 3: 2 pipes 1 stage Heat or 1 stage Cool MCO wiring diagram
Diagram showing connections for a 2-pipe 1-stage heat or 1-stage cool system, including terminals for valve, fan, remote setback, and remote sensor.
Typical wiring for ON/OFF control in 2 pipe heating/cooling (VC4013)
Typical wiring for ON/OFF control in 2 pipe heating/cooling (VC6013)
Application 4: 4 pipes 1 stage Heat and 1 stage Cool MCO/ACO wiring diagram
Diagram showing connections for a 4-pipe 1-stage heat and 1-stage cool system, including terminals for cool valve, heat valve, fan, remote setback, and remote sensor.
Fig.2.7 Typical wiring for ON/OFF control in 4 pipe 1H/1C Auto/Manual Change over (VC4013)
Typical wiring for 3-wire control in 4 pipe 1H/1C Auto/Manual Change over (VC6013)
Installation & Commissioning
- Pull wires through the wire hole. Loosen screw terminals, insert wires into the terminal block, and then retighten screws.
- Push the power box into the junction box.
Back Cover Installation
Install the thermostat approximately 5 feet (1.5m) above the floor in an area with good air circulation and average temperature.
Avoid installation locations affected by:
- Drafts or dead spots behind doors and in corners.
- Hot or cold air from ducts.
- Sunlight or radiant heat from appliances.
- Concealed pipes or chimneys.
- Unheated/uncooled areas, such as an outside wall behind the thermostat.
Diagrams illustrating the back cover installation:
- Place the back cover over the junction box, insert and tighten mounting screws.
- Insert the cable into the connector on the circuit board of the thermostat.
- Align the tabs on the back cover with the corresponding slots on the back of the thermostat, and then push until the thermostat snaps into place.
Installer System Test
After completing the installer setup, press the button again to begin a system test. Follow the procedure below to test the heating, cooling, and fan system.
Press and hold UP and DOWN buttons for 3 seconds to enter test mode.
Press UP or DOWN button to change system status.
Press UP button to advance to the next test number.
Press and hold UP and DOWN buttons to terminate the system test at any time.
System Test Status Examples:
- Heat: 0 = Heat turn off, 1 = Heat turns on.
- Cool: 0 = Cool off, 1 = Cool on.
- Fan: 0 = Fan off, 1 = Low speed Fan on, 2 = Medium speed Fan on, 3 = High speed Fan on.
- Thermostat Information (for reference only): Includes software revision, configuration identification codes, and production configuration dates.
An image of the thermostat display during a system test, showing 'System Test No.' and 'System' indicators.
Installer Set-Up (ISU) Setting
Press and hold MODE and FAN buttons simultaneously for 3 seconds to enter ISU.
Press UP or DOWN buttons to change settings.
Press FAN button to advance to the next function.
Press and hold UP and DOWN buttons for 3 seconds to exit and save settings.
An image of the thermostat display during Installer Set-Up (ISU), showing 'Number' and 'Setting' fields.
Setup Function Settings & Options
| Number | Description | Possible Options |
|---|---|---|
| 1 | System type | 0 Heat only, 1 Cool only, 2 two pipes 1H1C manual (Default), 4 four pipes manual, 5 four pipes auto |
| 5 | Remote sensor | 0 Onboard Sensor (Default), 1 Remote (NTC20K) |
| 9 | Temperature scale | 0 °F, 1 °C (Default) |
| 10 | Fan control type | 0 Cycle only, 1 Constant only (3 speed: Low->Med->High-> Low), 2 User can choose Cycle or Constant (3 speed: Low->Med->High->Auto-> Low) (Default) |
| 12 | Sequence Dead band for four pipes | 1 °C (2 °F), 1.5 °C (3 °F)(Default), 2 °C (4 °F), 3 °C (5 °F), 3.5 °C (6 °F), 4 °C (7 °F), 4.5 °C (8 °F), 5 °C (9 °F) |
| 13 | CPH value For Heat | 1, 2, 3, 4 (default), 5, 6, 7, 8, 9, 10, 11, 12 |
| 14 | CPH value For Cool | 1, 2, 3(default), 4, 5, 6 |
| 18 | Display Temperature adjustment | -2 °C(-4 °F), -1.5 °C(-3 °F), -1 °C(-2 °F), -0.5 °C(-1 °F), 0 °C(0 °F) (default), 0.5 °C(1 °F), 1 °C(2 °F), 1.5 °C(3 °F), 2 °C(4 °F) |
| 19 | Temperature Display mode | 0 display Room Temperature, 1 display Setpoint, 2 display both (default) |
| 20 | Heating Range Stops | 10-32 °C default 32 °C (50-90 °F default 90 °F) |
| 21 | Cooling Range Stops | 10-32 °C default 10 °C (50-90 °F default 50 °F) |
| 22 | Keypad Lockout | 0 All keys available(default), 1 System button Locked out, 2 Fan and System button Locked out, 3 All buttons locked out |
| 23 | Remote setback enable method | 0 Hotel card NO, 1 Hotel Card NC, 2 Button (Default) |
| 24 | Remote setback heating setpoint | Range 10-21°C Default: 18 °C (Range 50-70°F Default : 64) |
| 25 | Remote setback cooling setpoint | Range 22-32°C Default: 26 °C (Range 72-90 °F Default : 79 °F) |
| 27 | Freeze Protection | 0 Disabled (default), 1 Enabled |
Troubleshooting Tips
Heating system does not turn on:
- Set the mode to Heat by pressing the Mode button.
- Check that the heat temperature setting is above the room temperature and "Heat On" is displayed.
- Wait five minutes for the heating system to respond.
Cooling system does not turn on:
- Set the mode to Cool by pressing the Mode button.
- Check that the cool temperature setting is below the room temperature and "Cool On" is displayed.
- Wait five minutes for the cooling system to respond.
The fan doesn't work:
- Check if the Fan mode is set to Auto.
- Check if the heating or cooling system is working.
The Mode button doesn't work:
- Check if the keypad is locked.
- Check if the system is in Energy saving mode.
- Check if the thermostat is off.
The Fan button doesn't work:
- Check if the keypad is locked.
- Check if the system is in Energy saving mode.
- Check if the thermostat is off.
The Up or Down button doesn't work:
- Check if the keypad is locked.
- Check if the system is in Energy saving mode.
- Check if the thermostat is off.
Dimension
Diagrams showing the dimensions of the horizontal and vertical models of the T6861 thermostat, with measurements provided.
Horizontal model
Vertical model
