High
A3 on Viessmann Vitodens 111-W B1LD 35kW

The boiler has not been able to finish its startup checks because one of its safety sensors in the flue pipe is not fitted in the correct position, so it will not run until an 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 "Repairs").

From this model's manual
Verified against the Viessmann/Viessmann Vitodens 111 W B1ld 5697789 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

A1View →

All 28 fault codes on the Vitodens 111-W B1LD 35kW

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

0A0C1018303850515859A9b0b7b8E3E5F0F1F2F3F4F8F9FAFCFdFF

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