Low
d.33 on Vaillant Home System

Your boiler is displaying the real-time speed of the internal fan as part of its normal diagnostic checks, which is usually just an information code rather than a breakdown.

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

Fan speed target value: Current value in rpm. Fan speed=Display value x 100

DIY fix possible

No action required; this is an information code.Observe the display to confirm it clears once the check is complete.Restart the boiler if the code remains frozen for a long period.

Find a Gas Safe engineer
Search the official register →

Related fault codes

F.32View →d.34View →

Related guides you might find useful

Banging / kettling / whistling noise

Each noise points to a different fault.

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 →