Low Warning
S.40 on Vaillant ecoTEC Pro

Your boiler is temporarily running at a lower power level to prevent a fault and ensure it can still provide some warmth while it detects a minor issue.

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

Comfort protection active. The comfort protection mode is activated.

What causes this fault?

This happens when the boiler senses that its internal temperatures are rising too quickly or are inconsistent, often due to a slight buildup of debris or a sensor that is beginning to fail. Instead of shutting down completely, the boiler reduces its heat output to protect itself from damage while still trying to keep your home warm. It is essentially the boiler's way of 'limping' along until the underlying circulation or sensing issue is fixed.

DIY fix possible

Check for any other error codes on the displayMonitor the boiler to see if it returns to normal operation automaticallyEnsure all radiator valves are open to allow for maximum heat dissipationIf the message persists, book a routine service with a Gas Safe engineer to check sensor readings

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