Low Information
S.99 on Vaillant ecoTEC Pro 24

Your boiler is simply performing a routine internal check-up to ensure everything is working correctly and will resume normal operation shortly.

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

Vaillant self-test. The Vaillant self-test is activated.

What causes this fault?

This code appears when the boiler’s internal computer runs a temporary diagnostic check to verify that all sensors and safety components are communicating correctly. It is not triggered by a broken part, but rather a routine automated sequence that briefly pauses heating activity. Once the boiler confirms all systems are healthy, the code will clear and the unit will fire up as normal.

DIY fix possible

Wait for up to 15 minutes for the boiler to complete its automatic testMonitor the display to see if it returns to a normal temperature or status codeIf the code persists for over an hour, try turning the boiler off and on again once

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Related fault codes

S.30View →S.34View →

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