High
A3 on Viessmann Vitodens 200-W B2KB-35

Your boiler has stopped its setup check because a part that measures the temperature of the exhaust gases is not fitted in the right place, so it won't start up until a qualified engineer corrects it.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

What the manual says

Manufacturer manual

If the flue gas temperature sensor is positioned incorrectly, commissioning is cancelled and fault message A3 is displayed (see page 77).

From this model's manual
Verified against the Viessmann/Viessmann Vitodens 200 W B2hb B2kb 5792013 installation & service manual.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

Engineer required

This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Related fault codes

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All 89 fault codes on the Vitodens 200-W B2KB-35

Seeing a different code? Every code this model can display, in one place.

9A9b9C9E9F10181920283038505158597071737475768080/EE8181/EE8282/EE838485909192939495969899A7A9B0b1b5b7B8bFC1C2C3C4C5CdCFd3d4d5d6d7d8E0E1E2E3E4E5E7E8E9EAEbECEdEEEFF0F1F2F3F8F9FAFbFCFdFEFF

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