b30 High

Johnson Starley b30 Fault Code

Also written as B30 — same fault.

The Johnson Starley b30 fault code means: your boiler has temporarily stopped working because it cannot properly check that the fan is moving air and waste gases through the system.. It appears on 3 Johnson Starley models in our database.

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description: Air pressure switch blocked (blocking mode)
Typical repair cost £120-280 (including labour)

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Johnson Starley models that show the b30 fault code

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

Source

Johnson Starley b30 fault code information on this page is sourced and cross-checked against the official Johnson Starley service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026