BoilerFaultCodesVokera AL79 Fault Code
The Vokera AL79 fault code means: your boiler has shut down because it is getting too hot too quickly, usually because the water isn't moving through the system properly.. It appears on 6 Vokera models in our database.
Technical description: Flow temperature too high, or temperature differential between primary and return too high
What causes the Vokera AL79 fault?
This fault occurs when the water inside your boiler heats up much faster than the system can carry it away, causing the unit to overheat for safety. The most common reason is a pump failure or a blockage in the pipes, which prevents the hot water from circulating around your radiators. It can also be caused by a build-up of sludge or debris that restricted the flow through the main heat exchanger.
This fault is frequently seen at the start of autumn when heating systems are turned back on after a long summer break, as pumps can often seize up during periods of inactivity.
DIY fix possible
Check that your radiator valves are open and not turned to zero.Ensure your system pressure is between 1.0 and 1.5 bar on the pressure gauge.Try resetting the boiler by turning the mode selector switch to 'OFF/RESET' for a few seconds.
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Vokera models that show the AL79 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Vokera AL79 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