BoilerFaultCodesThe 6 most common faults
Your boiler has detected an internal safety issue and has shut itself down to prevent damage or unsafe operation.
Locate the reset button or dial on the boiler control panelPress or turn to the 'R' position for several seconds to reset the systemMonitor the display to see if the fault returns immediately
Your boiler has detected a sequence error during the ignition process and has shut down for safety to prevent a gas buildup.
Check that your gas emergency control valve is in the 'on' positionPress the reset button or turn the control knob to 'Reset' for 2 secondsVerify that other gas appliances in your home, like a hob, are working correctly
Your boiler has disabled the burner for safety reasons because it is failing to ignite or detect a flame properly.
Check if your gas supply is active by testing another gas appliance like a hobEnsure the condensate pipe (outside white plastic pipe) isn't frozen if it is cold outsidePress the Reset button on the control panel once
Your boiler has detected a sequence error during the ignition process and has shut down as a safety precaution.
Press the Reset button on the control panel once.Check that your gas pre-payment meter (if you have one) has credit.Ensure the gas supply valve to the boiler is fully open.
Your boiler is getting too hot and has shut down as a safety precaution to prevent damage.
Check that all radiator valves are fully openCheck that your boiler pressure is between 1.0 and 1.5 barBleed all radiators to remove trapped air which may be blocking water flow
Your boiler has detected that the pump is and not moving water through the system as it should, or there is air trapped inside preventing it from working.
Check that all radiator valves are openEnsure the system pressure is between 1.0 and 1.5 barCheck that there are no obvious leaks around the pump
on the Viessmann A8
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