Low
S.99 on Vaillant Home System

Your boiler has noticed the water pressure is low and is automatically refilling itself to the correct level.

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

Automatic filling active

From this model's manual
Verified against the Vaillant Home System installation & service manual, page 33.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

DIY fix possible

Wait for the boiler to finish the automatic filling processMonitor the pressure gauge to ensure it stays within the green zoneCheck visible radiators and pipework for any signs of water leaks

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