BoilerFaultCodesAlpha 0A43 Fault Code
The Alpha 0A43 fault code means: your boiler is currently unable to read the water temperature correctly because of a faulty internal sensor connection, which has caused it to stop heating your home as a safety precaution.. It appears on 3 Alpha models in our database.
Technical description: Return sensor short circuit.
What causes the Alpha 0A43 fault?
This fault occurs when the boiler's internal computer detects a broken electrical signal from the sensor that monitors cooled water returning to the unit. The most common reason is that the sensor's internal components have failed or the wiring connecting it to the main control board has become damaged or loose.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Alpha models that show the 0A43 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Alpha 0A43 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