BoilerFaultCodesThe 6 most common faults
01
02 High DIY-safe
Your boiler has shut down because it has detected an overheating issue and has locked itself for safety.
What to try first
Check that your home's radiator valves are open and not turned to the lowest setting.Ensure there is enough pressure in the system by checking the digital or needle gauge.Press the Reset button on the boiler control panel to see if the fault clears.
02
0A High Engineer
Your boiler has stopped working because it is not receiving enough gas to light the flame safely.
Full guide for 0A03
35 High Engineer
Your boiler has failed to ignite and cannot provide heating or hot water, likely because it hasn't detected a flame after several attempts.
Full guide for 3504
A2 High Engineer
Your boiler has stopped working because the fan is unable to clear air from the combustion chamber properly.
Full guide for A205
0C High Engineer
Your boiler has stopped working because the electricity supply it is receiving is weaker than it needs to operate safely.
Full guide for 0C06
F2 High Engineer
Your boiler has automatically shut down for safety because it detected that it has become dangerously overheated.
Full guide for F2on the Viessmann Vitopend 100
Circulation pumpOverheat thermostatTemperature sensors (NTC)Gas valveGas meter regulatorGas supply pipework
Based on parts cited in our fault code database. Your engineer will confirm what's actually needed after diagnosis.
Call a Gas Safe engineer if…
- You can smell gas or see signs of a leak
- The Viessmann shows an Emergency or High severity code
- The boiler keeps locking out after repeated resets
- You've tried the DIY checks and the fault hasn't cleared
- There's visible water leaking from the boiler
- The flame is yellow or orange instead of blue