BoilerFaultCodesThe 6 most common faults
Your boiler has failed to ignite or stay lit, meaning your heating and hot water have stopped working.
Why it happens: This fault occurs when the boiler's control system cannot confirm that a flame has been successfully established after several attempts. The most common reasons are a worn-out component that senses the flame, a lack of gas reaching the burner, or a build-up of carbon deposits on the ignition parts.
Check if your gas supply is active by testing another gas appliance like a hob.Try resetting the boiler using the 'R' or reset button on the control panel.Ensure your system pressure is between 1.0 and 1.5 bar on the pressure gauge.
Your boiler has switched itself off because it has reached a dangerously high temperature, likely due to a lack of water or poor circulation.
Why it happens: This fault occurs when the boiler's internal components detect that the heat being produced isn't being carried away quickly enough, causing the system to overheat. The most common reasons are a failed internal pump that isn't moving the water, or a significant blockage within the heat exchanger that is restricting flow. It can also be triggered by a large pocket of trapped air or a dangerously low water level in the system.
Check the pressure gauge and top up the water if it is below 1.5 barBleed all radiators to remove trapped air from the systemEnsure all radiator valves and isolation valves are fully openReset the boiler after checking water levels
Your boiler has shut down because it has detected it is getting too hot, which is usually caused by a lack of water or a circulation problem.
Why it happens: This fault occurs when the boiler's internal sensors detect that the heat exchanger has reached a dangerously high temperature, triggering a safety shutdown to prevent damage. The most common reasons are a failed internal pump that isn't moving water away from the burner quickly enough, or a significant air lock trap in the primary circuit. It can also be caused by a build-up of sludge blocking the flow of water through the narrow passages of the boiler.
Check the pressure gauge on your boiler and top up the water if it is below 1.5 barEnsure all your radiator valves are open and not switched offOnce the boiler has cooled down, press the 'Reset' button to see if the fault clears
Your boiler has failed to light the flame, which means it cannot provide any heating or hot water until the issue is resolved.
Why it happens: This fault occurs when the boiler's control system attempts to start the burner but cannot detect a flame after several attempts. The most common reasons are a lack of gas reaching the unit, worn-out spark electrodes that fail to ignite the gas, or a faulty sensor that cannot 'see' the flame even if it has successfully lit.
Check if other gas appliances in your home, like a hob, are working to confirm your gas supply is active.Ensure your gas meter has credit if you use a prepay meter.Press the Reset button on the boiler control panel once to see if the fault clears.
Your boiler's internal computer has crashed due to an ignition failure or electrical interference, preventing it from starting the burner.
Why it happens: This fault occurs when the boiler's internal computer experiences a critical communication error or fails to verify the ignition process. The most common reasons are worn-out spark electrodes that can no longer light the gas, or electrical 'noise' from nearby appliances interfering with the boiler's sensitive electronics.
Press the reset button or turn the boiler off and back on at the fused spur switchEnsure large electronic devices or powerful wireless routers are not sitting directly next to the boilerCheck if other gas appliances in your home are working to ensure gas is reaching the property
Your boiler has shut itself down as a safety precaution because it has detected an overheating issue within the system.
Why it happens: This fault occurs when the water inside the boiler reaches an unsafe temperature, triggering a safety sensor to cut the power to the burner. The most common reasons include a failing pump that isn't moving water away from the burner quickly enough, or a buildup of debris and sludge that is restricting flow through the heat exchanger.
Full guide for 02on the Viessmann Vitodens 050-W
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
Avoid the next call-out bill
Monthly cover means no unexpected bills when your boiler breaks down.
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