High Lockout
d3 on Worcester Bosch Greenstar 25 HE Combi

Your boiler has lost its connection to an external safety device or a specific internal link that tells it how to operate safely.

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.

Technical description

External temperature limiter tripped (link LR-Ls on Heatronic missing)

What causes this fault?

This fault occurs when the electrical connection that bridges the safety circuit on the boiler's control board is broken or missing. It is often caused by a loose wiring connection to your external thermostat, a damaged link plug, or a vibration-induced failure of the circuit board. Without this continuous connection, the boiler shuts down immediately as a safety precaution because it cannot confirm if external controls are allowing it to fire.

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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Related fault codes

C1View →C6View →EAView →

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