S.16 Low

Glow-worm S.16 Fault Code

Also written as S16 — same fault.

The Glow-worm S.16 fault code means: your boiler is performing a routine cooling cycle to clear internal gases after a burst of activity and is not currently in a fault state.. It appears on 26 Glow-worm models in our database.

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.

Technical description: fan overrun

What causes the Glow-worm S.16 fault?

This occurs when the boiler’s fan continues to run after the burner has switched off to safely purge remaining heat and combustion gases from the unit. It is a normal safety process that typically happens after a period of intense heating or hot water demand to ensure the internal components cool down correctly. Your boiler hasn't broken down; it is simply finishing its work cycle before it can start again.

DIY fix possible

Wait for 5-10 minutes to allow the cooling cycle to completeEnsure your thermostat is not calling for heat if you want the fan to stop soonerCheck that the boiler display changes to a different code after the cooling period

Find a Gas Safe engineer

Search the official register for a qualified engineer in your area.

Gas Safe Register →
Boiler cover options

Avoid the next call-out bill

A cover plan would handle faults like S.16: no call-out fees, no surprise bills.

Approved partner
Domestic Appliance Guard
Unlimited call-outs, 24/7 helpline, no price-hike promise
Get a quote →

Affiliate links. We may earn a commission at no extra cost to you.

Glow-worm models that show the S.16 fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Glow-worm S.16 fault code information on this page is sourced and cross-checked against the official Glow-worm service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026