Thermostat shows B2 and cannot control a specific zone valve or actuator in a multi‑zone system.

Safety first: Turn off power to the heating control module and actuators before working on wiring.

• Identify affected zone: Use the thermostat or app to determine which zone is reporting the B2 error.
• Check actuator wiring: At the manifold or valve, verify that the actuator’s wires are securely connected to the correct zone terminals on the Viessmann zone control module.
• Test actuator operation: With power restored, call for heat in that zone and feel the actuator or valve body to see if it warms or moves after a few minutes. No response suggests a failed actuator or output.
• Swap actuators (if possible): Swap the suspect actuator with a known good one from another zone. If the error follows the actuator, replace it. If it stays with the zone, the control output may be faulty.
• Check configuration: In the installer menu, confirm that the zone is correctly assigned to the thermostat and that the output type matches the actuator (e.g. thermal 230 V or 24 V as per system design).