B5
Viessmann
Cooling Mode Configuration or Communication Fault
Thermostat displays B5 and cannot control cooling mode in a reversible heat pump system.
Advertisements
Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
Advertisements
Possible Causes
Cooling mode disabled in boiler/heat pump configuration, Thermostat not assigned to cooling circuit, Firmware not supporting cooling on this model, Communication error with heat pump controller
How to Fix / Troubleshooting
Safety first: Do not open the heat pump cabinet. Only use user and installer menus.
- Check cooling enable setting: In the boiler/heat pump controller menu, verify that cooling mode is enabled and that the thermostat is allowed to request cooling.
- Verify thermostat mode: Ensure the thermostat is set to heating & cooling mode, not heating‑only.
- Confirm circuit assignment: In installer settings, assign the thermostat to the correct cooling circuit if separate from heating.
- Update firmware: Check for firmware updates for both thermostat and heat pump controller that may add or fix cooling support.
- Contact installer: If B5 remains, a professional may need to re‑commission the system for cooling operation.
Advertisements
Repair Difficulty
Hard
4/5
Advertisements