A10
Herz
Flow Switch / Flow Sensor Fault
Boiler shows A10, no heating, pump may run continuously
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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 Herz flow switch, blocked system filter, air lock in primary circuit, defective electronic flow sensor
How to Fix / Troubleshooting
Safety: Turn off power and allow the system to cool. Some water spillage is possible when opening components.
- Check system pressure: Ensure the pressure is within Herz specifications. Low pressure can prevent flow detection.
- Bleed air: Bleed radiators and the automatic air vent to remove trapped air that can stop flow.
- Clean system filter: If a Herz system filter or dirt separator is installed on the return, isolate, remove, and clean the filter screen.
- Inspect flow switch: On models with a mechanical flow switch, remove and check that the paddle or turbine moves freely. Clean debris and refit.
- Persistent A10: Replace the Herz flow sensor/switch assembly.
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Repair Difficulty
Medium
3/5
Required Part
Herz primary flow sensor/switch
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