Low
02 on Biasi Dina

Your boiler is currently running a manual test mode designed for engineers to check performance, and it is not a standard functional fault.

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

Activation of the chimney sweep function at maximum DHW output (under P06)

DIY fix possible

Switch the boiler to the 'Off' or 'Standby' positionWait 30 secondsSwitch the boiler back to the 'On' or 'Winter/Summer' mode to exit the test sequence

Find a Gas Safe engineer
Search the official register →

Related fault codes

01View →

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 →