High
Reset light on Glow-worm Micron 50FF

Your boiler has switched itself off because it got too hot, likely triggered by a safety sensor to prevent damage.

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

If the overheat Safety Temperature Limiter operates as indicated by illuminated reset light, open the controls cover and turn temperature control to “0” (anticlockwise) and then back to original position.

From this model's manual
Verified against the Glow Worm Micron 50ff 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 boiler reaches an unsafe temperature, forcing the system to shut down for safety. It is usually caused by a failure to move heat away from the boiler quickly enough, often due to a broken pump or a blockage in the internal pipework. In some cases, a faulty sensor may mistakenly signal that the unit is overheating even when temperatures are normal.

This issue is more frequent during the first cold snap of autumn when pumps that have been idle all summer often seize up upon being switched back on.

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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