Communication problems — System controller cannot talk to slave thermostat

What does Communication problems mean?

The slave thermostat may not correctly indicate equipment fan operation, the current system mode, or time of day. The system controller might fail to verify communications with the slave thermostat, or the thermostat operates continuously in setback or comfort modes despite proper configuration.

• Improper configuration of system devices, including an incorrect slave thermostat device address.
• Faulty wiring or failure of a single device connected to the communication bus.
• Incorrectly configured communication-related options on the system controller or devices (e.g., 2400 Baud Rate option mismatch).
• Protruding screw heads or bent interior standoffs on the slave thermostat causing set point buttons to be constantly pressed.
• Incorrect communication bus wire connections (red, green, and black wires are not in proper locations) or a faulty ribbon cable/wiring connector board.

Click steps to track your progress.

1. 1

   Check the device address of the slave thermostat, ensuring it is below the associated system controller and within its scanning range (see Table 1).

2. 2

   Verify the configuration of all communication-related options for the system controller and each device in the problem system.

3. 3

   Ensure the '2400 Baud Rate' option for each device is configured the same and the rotary switch for each device is at position 0.

4. 4

   Inspect the slave thermostat's mounting and cover plates for protruding screw heads or bent interior standoffs that might depress set point buttons.

5. 5

   Check the slave thermostat wiring connector board for correct communication bus wire connections (red, green, black) and refer to page 9 for ribbon cable and wiring connector block troubleshooting.