S.52 Low

Vaillant S.52 Fault Code

Also written as S52 — same fault.

The Vaillant S.52 fault code means: your boiler is in a waiting period because the air or flue system has detected a minor issue while trying to start up.. It appears on 7 Vaillant models in our database.

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: Burner/electrode check - check ignition system and flame sensing electrodes

What causes the Vaillant S.52 fault?

This fault occurs when the boiler's internal safety sensors detect a delay or minor obstruction in the air flow needed for combustion. It is typically caused by a tiring fan that is struggling to reach the correct speed or an air pressure switch that is failing to click over. The boiler pauses its startup sequence to ensure it can exhaust waste gases safely before fully firing up.

This issue can be more frequent during windy weather, as high gusts can occasionally interfere with the pressure signals at the external flue terminal.

Typical repair cost £90-250 (including labour)

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Vaillant models that show the S.52 fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Vaillant S.52 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