Thermostat displays C3 and indicates that the heating circuit pump feedback is invalid; pump status cannot be monitored.

Safety first: Turn off power to the boiler and pump circuits before working on wiring. Pumps may start unexpectedly.

• Check configuration: In the boiler or system controller menu, ensure that pump feedback is only enabled if a compatible pump with feedback contact is installed.
• Inspect feedback wiring: Verify that the feedback contact from the pump is wired to the correct input terminals on the controller.
• Test pump operation: Confirm that the pump actually runs when there is a heat demand, even if feedback is faulty.
• Disable feedback (if allowed): If the pump does not provide feedback, disable this feature in the configuration to clear the error.
• Replace pump or controller input: If feedback is required and wiring is correct, a technician may need to replace the pump or controller.