BoilerFaultCodesThe 6 most common faults
Your boiler has shut down because it has detected an overheating issue and has locked itself for safety.
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.
Your boiler has detected an issue with the gas supply pressure and has shut down as a safety precaution.
Check if other gas appliances, like a gas hob, are working correctly to confirm fuel supply.Ensure the gas stopcock valve is fully open at your gas meter.Press the 'Reset' button or turn the control dial to 'Reset' once and wait for the boiler to restart.
Your boiler has detected a communication or ignition fault and has shut down as a safety precaution to prevent damage.
Locate the reset button or dial on the front control panelPress or turn to 'Reset' for several seconds and releaseWait for the boiler to attempt to restart; if the code returns immediately, contact a gas safe engineer
Your boiler is getting too hot too quickly, which is usually caused by water not flowing through the system properly.
Check that all radiator valves are fully openEnsure the boiler pressure is between 1.0 and 1.5 barBleed your radiators to remove any trapped air
Your boiler is stuck in a self-diagnostic test mode and is unable to move into its normal heating cycle.
Turn the boiler power switch to 'OFF' for 30 secondsTurn the power switch back to 'ON'If the code persists, turn the main mode selector dial to 'Reset' for 3 seconds and release
Your boiler has detected that the internal pump is stuck or there is very little water pressure, preventing it from heating your home.
Check the pressure gauge and top it up to 1.5 bar using the filling loopEnsure all radiator valves and isolation valves are fully openRestart the boiler to see if the pump clears itself
on the Viessmann Vitopend 100
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