BoilerFaultCodesVokera AL73 Fault Code
The Vokera AL73 fault code means: your boiler has detected a problem with the sensor that monitors the temperature of the water returning to the unit, which is preventing it from running safely.. It appears on 6 Vokera models in our database.
Technical description: Return thermistor fault
What causes the Vokera AL73 fault?
This fault occurs when the boiler's internal computer receives an incorrect or missing signal from the sensor that monitors water temperature coming back from your radiators. The most common reason is that the sensor itself has worn out or developed a spiritual electrical fault, though it can also be triggered by loose or damaged wiring between the sensor and the main control board.
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 →Avoid the next call-out bill
A cover plan would handle faults like AL73: no call-out fees, no surprise bills.
Affiliate links. We may earn a commission at no extra cost to you.
Vokera models that show the AL73 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Vokera AL73 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 7 July 2026