166 High

Baxi 166 Fault Code

The Baxi 166 fault code means: your boiler has detected an issue with the way it is venting or drawing air, causing it to shut down for safety.. It appears on 26 Baxi models in our database.

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.

Technical description: Air pressure switch fault

What causes the Baxi 166 fault?

This fault occurs when the boiler's internal safety sensors detect that the fan isn't moving enough air to safely clear exhaust fumes or pull in fresh oxygen. The most common reasons are a blockage in the flue pipe outside, a build-up of debris in the internal tubes, or a mechanical failure of the switch that monitors air pressure.

This fault is more common during periods of high winds or extreme cold, as external debris can blow into the flue or ice can restrict the air intake.

Typical repair cost £120-220 (including labour)

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Baxi models that show the 166 fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Baxi 166 fault code information on this page is sourced and cross-checked against the official Baxi service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026