A02
Herz
Flame Loss During Operation
Boiler starts, flame appears briefly then shuts down and locks out with code A02
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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
Unstable gas pressure at Herz gas valve, partially blocked Herz burner, faulty flame detection electrode, flue gas recirculation due to blocked flue
How to Fix / Troubleshooting
Safety: Isolate electrical power and close the gas valve before opening the combustion chamber. Work only when the boiler is cool.
- Visual flame check: Through the inspection window, observe the flame when the boiler starts. A noisy, lifting, or yellow flame suggests combustion issues.
- Clean burner: Remove the Herz burner head as per the service manual. Gently brush and vacuum the burner surface and check for corrosion or deformation.
- Inspect ionisation electrode: Ensure the electrode is correctly positioned in the flame and its cable is firmly connected to the control board.
- Check flue and air intake: Inspect the concentric flue terminal for obstructions (leaves, nests, ice). Make sure the air intake is not blocked.
- Persistent A02: Gas valve modulation or control board may be defective. This requires combustion analysis and adjustment by a certified Herz technician.
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Repair Difficulty
Hard
4/5
Required Part
Herz premix gas burner
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