Low
d.39 on Glow-worm Sustain 12s

Your boiler is simply reporting the current temperature of the water heated by your solar panels, which is a normal operational reading rather than an actual fault.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Monitor it

This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.

What the manual says

Manufacturer manual

Water temperature in the solar circuit

From this model's manual
Verified against the Glow Worm Sustain 12s installation & service manual, page 30.
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 fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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