Abgastemperatursensor nicht richtig positioniert
The A3 error code on Viessmann boilers indicates abgastemperatursensor nicht richtig positioniert. Symptoms include brenner blockiert.
Viessmann A3 means: abgastemperatursensor nicht richtig positioniert. The usual cause is temperature sensor or replace the faulty flue gas. A Gas Safe registered engineer should diagnose the root cause.
What Does A3 Mean
The A3 code is shown by the boiler’s control board when it detects abgastemperatursensor nicht richtig positioniert. The boiler then stops instead of continuing to run in that condition: the code is the appliance reporting a problem, not proof that the boiler is broken.
| What you see on the boiler |
|---|
| Brenner blockiert |
Common Causes
Causes documented in 24 technical sources.
| Cause |
|---|
| temperature sensor or replace the faulty flue gas |
Safety Warning
A3 is a gas-related fault. Never attempt to repair or adjust the gas valve, burner assembly, or flue system yourself. All gas work must be carried out by a Gas Safe registered engineer (UK) or licensed HVAC technician (US). Repeated resets after ignition failure can cause unburnt gas to accumulate inside the combustion chamber — this is a serious safety hazard. If you smell gas at any point, turn off the gas supply at the meter, open windows, leave the property, and call your gas emergency service immediately. Gasbezogener Störungscode. Öffnen Sie das Gerätegehäuse nicht und versuchen Sie nicht, Gasventil, Brenner, Zündanlage oder Abgassystem selbst zu reparieren. Wiederholtes Entriegeln ist unsicher. Diagnose und Reparatur müssen von einem Fachbetrieb durchgeführt werden.
Parts & Prices
Prices shown are indicative. Actual prices and availability vary by region.
How to Fix It
Abgastemperatursensor richtig einbauen
Refer to the Viessmann service documentation for the detailed procedure. Only a qualified engineer should carry out these repairs.
Diagnostic Tools
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Affected Models
Viessmann models that can display fault code A3:
| Model Family | Output Range | Frequency |
|---|---|---|
| All Viessmann models | — | Possible |
Frequently Asked Questions
Abgastemperatursensor richtig einbauen. According to the technical documentation, this is the first check on the list for A3.
A3 is classified as a high-severity fault: it involves gas, combustion or flue components. Do not keep resetting the boiler and do not attempt the repair yourself — call a Gas Safe registered engineer.