High
Reset light (illuminated) on Glow-worm Micron 40FF

Your boiler has become too hot and has automatically shut down to protect itself, usually because the water inside isn't circulating properly.

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

Overheat safety cutoff device may need resetting

From this model's manual
Verified against the Micron 80ff 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.

What causes this fault?

This fault occurs when the water inside the heat exchanger reaches a dangerously high temperature, triggering a safety switch to cut off the burner. The most common reason is a failure in the circulation pump or a blockage in the pipes, which prevents the heat from being carried away to your radiators. It can also be caused by air trapped in the system or a faulty sensor incorrectly reading the temperature.

This issue often surfaces at the start of autumn when the heating is turned back on after a long summer break, as pump components can seize up during periods of inactivity.

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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