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.

Technical description

Automatic filling active

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

Find a Gas Safe engineer
Search the official register →

Related fault codes

F.22View →S.91View →S.98View →

Related guides you might find useful

Boiler keeps losing pressure

Six most common causes of dropping pressure.

Read →

Yellow or orange flame — CO safety

Safety-critical — turn off, read this.

Read →

Is boiler cover worth it?

Break-even maths on monthly cover.

Read →