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 shut down because it has overheated or detected a lack of water flow through the system.
Why it happens: This fault occurs when the boiler's internal temperature reaches a dangerously high level, triggering a safety shutdown to prevent damage. The most common reasons are a pump failure that stops water from moving or a buildup of air and sludge that creates a blockage in the heat exchanger. Essentially, the burner is creating heat, but the system cannot move that heat away quickly enough.
Check the pressure gauge and top up water if it is below 1.5 barBleed your radiators to remove trapped airPress the 'Reset' or 'E' button to restart the boiler
Your boiler has shut down because electronic interference or a faulty internal circuit board is preventing the burner from starting safely.
Why it happens: This fault occurs when the boiler's internal computer receives garbled or 'noisy' signals that prevent it from safely managing the burner. It is typically caused by electronic interference from a nearby appliance or a physical defect in the PCB or its unique coding card. Essentially, the boiler has lost its ability to verify its own settings and shuts down as a safety precaution.
Turn off any nearby large electrical appliances or power tools that might cause electronic interference.Press the reset button or turn the boiler off and back on at the fused spur.If the fault persists after a reset, you must call a Gas Safe registered engineer.
Your boiler has detected a sequence of ignition or flame detection errors and has shut itself down for safety.
Why it happens: This fault occurs when the boiler's internal computer fails to detect a reliable flame during the ignition process. The most common reasons are worn-out sparks that can no longer light the gas, or a dirty sensor that cannot 'see' the flame even after it has started. It can also be caused by a lack of gas reaching the burner due to a faulty valve or a blockage in the air supply.
Full guide for 04Your boiler has detected a sequence of ignition or flame detection errors and has shut itself down for safety.
Why it happens: This fault occurs when the boiler's internal computer fails to detect a reliable flame during the ignition process. The most common reasons are worn-out sparks that can no longer light the gas, or a dirty sensor that cannot 'see' the flame even after it has started. It can also be caused by a lack of gas reaching the burner due to a faulty valve or a blockage in the air supply.
Full guide for 06Your boiler has detected a sequence of ignition or flame detection errors and has shut itself down for safety.
Why it happens: This fault occurs when the boiler's internal computer fails to detect a reliable flame during the ignition process. The most common reasons are worn-out sparks that can no longer light the gas, or a dirty sensor that cannot 'see' the flame even after it has started. It can also be caused by a lack of gas reaching the burner due to a faulty valve or a blockage in the air supply.
Full guide for 08on the Viessmann Vitodens 333-F
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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