P33 Medium

Alpha P33 Fault Code

The Alpha P33 fault code means: your boiler is failing to switch off when the house reaches the target temperature, meaning your radiators will stay on until you manually turn the boiler down.. It appears on 4 Alpha models in our database.

Book a service

This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.

Technical description: The optional environment thermostat (TA) not working, the boiler functions all the time in central heating mode. (Can be activated through the 'Customisation' menu. It allows activation of the central heating even if the TA is out of order).
Typical repair cost £120-250 (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 P33 fault code

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

Source

Alpha P33 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