BoilerFaultCodesVokera AL28 Fault Code
The Vokera AL28 fault code means: your boiler has detected that the water coming back from your radiators is hotter than the water going out, which usually means the water isn't circulating correctly or a sensor is faulty.. It appears on 8 Vokera models in our database.
Technical description: Temperature differential inverted (return sensor temperature higher than flowsensor temperature)
What causes the Vokera AL28 fault?
This fault occurs when the boiler's internal sensors detect that the water returning from your radiators is hotter than the water being sent out, which is physically impossible in a healthy system. The most common reason is a blockage or a pump failure preventing water from moving, though it is often caused by one of the temperature sensors simply failing and sending the wrong information to the control board.
This issue often surfaces in autumn when the heating is turned on for the first time after summer, as pump components can seize up during long periods of inactivity.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Gas Safe Register →Vokera models that show the AL28 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Vokera AL28 fault code information on this page is sourced and cross-checked against the official Vokera service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026