BoilerFaultCodesVokera b25 Fault Code
Also written as B25 — same fault.
The Vokera b25 fault code means: your boiler has detected that the water is heating up too quickly, which usually means it can't circulate water through the system properly.. It appears on 1 Vokera model in our database.
Technical description: Excessive temperature rise
What causes the Vokera b25 fault?
This fault occurs when the heat inside the boiler builds up much faster than the water can carry it away. The most common reason is a blockage or a failing pump preventing the water from flowing through the pipes and radiators effectively. It can also be caused by a build-up of sludge or debris inside the main heat exchanger, which restricts the water path.
This fault is frequently seen at the start of autumn when heating systems are turned back on after being idle all summer, which can cause internal pump parts to seize.
DIY fix possible
Check that your radiator valves are open and not turned to zero.Ensure your boiler pressure is between 1 and 1.5 bar on the gauge.Try resetting the boiler to see if the fault clears.
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Gas Safe Register →Vokera models that show the b25 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Vokera b25 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