How much does it cost to fix Vokera error code b 18?

Typical repair cost for the Vokera b 18 fault is £150-300 including labour.

b 18 Emergency

Vokera b 18 Fault Code

Q: What does the Vokera b 18 fault code mean?

Your boiler has detected that the water inside the unit is dangerously hot and has shut itself down to prevent damage or overheating.

Also written as B18 — same fault.

The Vokera b 18 fault code means: your boiler has detected that the water inside the unit is dangerously hot and has shut itself down to prevent damage or overheating.. It appears on 1 Vokera model in our database.

Technical description: Flow sensor above 95 °C

What causes the Vokera b 18 fault?

This fault occurs when the water leaving the boiler exceeds a safe temperature limit, causing the system to shut down to protect itself. The most common reason is a lack of water circulation, often caused by a failing pump or a blockage within the main heat exchanger that prevents heat from being carried away quickly enough.

This issue is more common during the first cold spell of autumn, when pumps that have sat idle all summer can seize up or struggle to move heavy sludge that has settled in the radiators.

Typical repair cost £150-300 (including labour)

DIY fix possible

Check that all radiator valves are fully openEnsure the boiler pressure is between 1.0 and 1.5 barReset the boiler following the manufacturer instructions once it has cooled down

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Vokera models that show the b 18 fault code

Click a model for the full fault code list and model-specific repair notes.

Hydra Repair: £150-300

Source

Vokera b 18 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