Low
Vitotronic 300 on Viessmann Vitopend 111

Your boiler's outdoor temperature sensor has triggered an automatic frost protection mode to prevent your pipes from freezing.

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

Activates after 0°C / 32°F outdoor temperature

DIY fix possible

Check that the outdoor sensor is not covered by snow or iceMonitor the boiler to ensure it returns to normal operation once the 'frost' ice crystal symbol disappearsEnsure your thermostat is set to a comfortable temperature to maintain heat flow

Find a Gas Safe engineer
Search the official register →

Related guides you might find useful

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 →

New boiler cost 2026

Realistic UK prices for a swap.

Read →