A11
Herz
Flue Gas Temperature Too High
Boiler display shows A11, burner stops, fan may continue to run
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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
Blocked or undersized flue on Herz boiler, fouled primary heat exchanger, incorrect gas rate causing overfiring, faulty flue gas temperature sensor
How to Fix / Troubleshooting
Safety: Turn off the boiler and do not operate it if flue gas overheat is indicated. Risk of flue gas spillage.
- Inspect flue externally: Check for visible damage, sagging, or blockage at the terminal.
- Clean heat exchanger: Remove the burner and access the primary heat exchanger. Brush and vacuum combustion surfaces as per Herz instructions.
- Check flue gas sensor: Locate the flue gas NTC or thermostat on the flue hood. Ensure it is firmly attached and its wiring is intact.
- Do not alter gas settings: Gas rate and combustion must be checked with instruments by a qualified Herz technician. If A11 persists, arrange professional service.
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Repair Difficulty
Professional Required
5/5
Required Part
Herz flue gas temperature sensor
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