High
Red LED illuminated on Halstead Finest Gold

Your boiler has detected a safety fault and has locked itself to prevent operation, meaning you currently have no heating or hot water.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

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.

What the manual says

Manufacturer manual

Safety Lockout. There is a fault condition preventing operation of the appliance (e.g., air pressure switch, water flow switch, or overheat thermostat fault during power up).

From this model's manual
Verified against the Halstead Finest Gold ISM installation & service manual.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

Engineer required

This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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