How much does it cost to fix Alpha error code 29?

Typical repair cost for the Alpha 29 fault is £120-220 including labour.

29 High

Alpha 29 Fault Code

Q: What does the Alpha 29 fault code mean?

Your boiler has detected a problem with the sensor that monitors exhaust gases, and it has shut down for safety purposes.

The Alpha 29 fault code means: your boiler has detected a problem with the sensor that monitors exhaust gases, and it has shut down for safety purposes.. It appears on 25 Alpha models in our database.

Technical description: Flue sensor fault

What causes the Alpha 29 fault?

This fault occurs when the sensor responsible for measuring the temperature of the exhaust gases signals that it is failing or providing an unrealistic reading. The most common reason is that the sensor has developed an electrical fault due to age, or the internal wiring has become damaged over time. Because this sensor is a critical safety component that prevents the boiler from overheating, the system will shut down immediately to prevent damage.

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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Alpha models that show the 29 fault code

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

Source

Alpha 29 fault code information on this page is sourced and cross-checked against the official Alpha service / installation manuals for each affected model.

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