BoilerFaultCodesVokera b18 Fault Code
Also written as B18 — same fault.
The Vokera b18 fault code means: your boiler has reached an excessively high temperature and has shut down as a safety precaution to prevent overheating.. It appears on 1 Vokera model in our database.
Technical description: Flow sensor above 95 °C
What causes the Vokera b18 fault?
This fault occurs when the water leaving the boiler gets too hot, causing the system to shut down to prevent damage. The most common reason is a lack of water flow, often caused by a failing pump or a blockage in the pipework that prevents heat from being carried away from the boiler quickly enough.
This issue is more frequent during the first cold snap of autumn when heating systems are turned back on after sitting idle, which can cause internal pumps to seize.
DIY fix possible
Check that your radiator valves are open to allow water to circulateCheck that the system pressure is between 1.0 and 1.5 bar on the gaugeTurn the boiler off and wait 30 minutes for it to cool down before resetting
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Gas Safe Register →Vokera models that show the b18 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Vokera b18 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