Medium Warning
High neon light on Glow-worm EnergySaver

Your boiler's status light indicates it is running at its maximum heating power, but if the light remains off while the boiler is struggling, there may be an internal electrical communication fault.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

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This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.

Technical description

High flame indicator. If not lit, check continuity between 4 and 1 on High/Low switch.

What causes this fault?

This occurs when the boiler is commanded to run at its highest heat output but the electrical signal fails to register. The most common reason is a mechanical failure in the high/low switch or a break in the wiring that prevents the system from confirming the flame level. This results in the boiler being unable to modulate its power correctly to meet the demands of your heating system.

This issue is often more noticeable during the first cold spell of autumn when the boiler is required to switch from low-power water heating to high-power central heating.

Engineer required

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

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Related fault codes

Low neon lightView →

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