Viessmann
Single Zone or Actuator Failure
Radiators or underfloor loops in one zone stay cold while others heat normally; no error code on thermostat.
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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.
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Possible Causes
Stuck or failed zone valve/actuator, Airlock in that part of the system, Closed manual valve on manifold, Misassigned zone in thermostat configuration
How to Fix / Troubleshooting
Safety first: Turn off power before touching actuators or valves. Water in the system may be hot.
- Check zone assignment: Ensure the thermostat is correctly assigned to control that specific zone in the configuration.
- Inspect actuators/valves: At the manifold or radiator, verify that the actuator or valve is installed and wired correctly. Feel for warmth when the zone is calling for heat.
- Open manual valves: Make sure any manual isolation valves on the manifold or radiator are fully open.
- Bleed air: Bleed radiators or manifolds to remove trapped air that can block flow.
- Replace actuator/valve: If the actuator does not open when powered, replace it with a compatible Viessmann zone actuator.
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Repair Difficulty
Medium
3/5
Required Part
Viessmann zone actuator or zone valve
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