Low
S.01 on Vaillant ecoTEC Plus 938

Your boiler is performing a normal startup procedure by clearing out the combustion chamber before it begins heating your home.

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

Heatingmode:Advancefanoperation

From this model's manual
Verified against the Vaillant Ecotec Plus 826 installation & service manual, page 47.
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 is a brief preparatory phase where the boiler's fan spins up to push air through the system and clear any leftover gases from the burner area. It is a necessary safety check to ensure the chamber is fresh and ready for a clean ignition. This is not a malfunction, but rather a standard step in the sequence before the heating starts.

DIY fix possible

This fault may be fixable without an engineer. Check your manual first.

Find a Gas Safe engineer
Search the official register →
Boiler cover options

Avoid the next call-out bill

A cover plan would handle faults like S.01: 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.

Related fault codes

S.02View →S.04View →

Related guides you might find useful

Yellow or orange flame — CO safety

Safety-critical — turn off, read this.

Read →

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 →