Low Warning
9b:70 on Viessmann Vitodens 333-F

Your boiler has detected an incorrect setting or a communication error regarding the minimum water temperature required when an external control system asks for heat.

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

Minimum set boiler water temperature in case of external demand

What causes this fault?

This fault occurs when there is a mismatch between the boiler's internal computer and the external smart controls or thermostat. It usually happens because the minimum heat level requested by the external system is set higher than what the boiler is programmed to allow, causing a configuration conflict.

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

Find a Gas Safe engineer
Search the official register →

Related guides you might find useful

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 →

When to replace your boiler

7 signs repair isn't worth it anymore.

Read →