d4:0 Low

Viessmann d4:0 Fault Code

Also written as D40 — same fault.

The Viessmann d4:0 fault code means: your boiler is telling you that the heating system settings are currently turned down to zero, which means it will not provide any heat to your radiators.. It appears on 6 Viessmann 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: Heating curve level = 0

DIY fix possible

Locate the main display panel on your boiler.Access the 'Heating' or 'Comfort' menu settings.Adjust the heating curve or target room temperature to a value above zero.

Find a Gas Safe engineer

Search the official register for a qualified engineer in your area.

Gas Safe Register →

Viessmann models that show the d4:0 fault code

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

Source

Viessmann d4:0 fault code information on this page is sourced and cross-checked against the official Viessmann service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026