Low
S.10 on Vaillant ecoTEC sustain

Your boiler is simply letting you know that it is currently busy heating up water for your taps or shower.

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.

Technical description

Hot water handling mode: Requirement

DIY fix possible

No action required, this is a normal operating status and not a fault code.

Find a Gas Safe engineer
Search the official register →

Related fault codes

S.11View →

Related guides you might find useful

Is boiler cover worth it?

Break-even maths on monthly cover.

Read →

When to replace your boiler

7 signs repair isn't worth it anymore.

Read →

New boiler cost 2026

Realistic UK prices for a swap.

Read →