BoilerFaultCodesVaillant S.57 Fault Code
Also written as S57 — same fault.
The Vaillant S.57 fault code means: your boiler has temporarily paused operation to prevent potential overheating and will restart automatically once it has cooled down.. It appears on 9 Vaillant models in our database.
Technical description: Waiting period comfort safety mode
What causes the Vaillant S.57 fault?
This status occurs when the boiler's internal sensors detect that the heat exchanger is getting too hot too quickly, prompting the system to pause to protect itself. It is usually caused by a temporary restriction in water flow or a minor mismatch between the heat being produced and how fast the pump can move it away. Once the temperature drops to a safe level, the boiler will automatically resume normal operation without needing a manual reset.
This code is more common during the first few cold spells of autumn when the heating is turned back on after a long summer break, often due to a slightly sluggish pump or air trapped in the radiators.
DIY fix possible
Check that all radiator valves are fully open to allow water to flow freelyEnsure there are no obstructions around the external flue pipeMonitor the boiler for several minutes to see if it clears the code and restarts on its own
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Gas Safe Register →Vaillant models that show the S.57 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Vaillant S.57 fault code information on this page is sourced and cross-checked against the official Vaillant service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026