Low
S.23 on Vaillant ecoTEC Plus 620

Your boiler is currently preparing the burner to provide hot water, which is a normal part of its operation.

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

Hotwaterhandlingmode:Burnerignition

From this model's manual
Verified against the Vaillant Ecotec Plus 615 installation & service manual, page 38.
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 code appears when the boiler detects a demand for hot water and is physically firing up the burner to meet that request. It is a normal part of the start-up sequence and indicates that the internal components are working correctly to heat your water. You will typically see this briefly on the display every time you turn on a hot tap or shower.

DIY fix possible

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

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Related fault codes

S.20View →S.21View →S.24View →

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