BoilerFaultCodesThe 6 most common faults
Your boiler has failed to light because it cannot detect a flame or is struggling to vent correctly.
Why it happens: This fault occurs when the boiler attempts to start up but fails to sense a flame after several attempts. The most common reasons are a lack of gas reaching the burner, a faulty spark electrode that can't ignite the fuel, or a blockage in the chimney pipe preventing the air flow needed for combustion.
Check if other gas appliances in your home, like a cooker, are working.Ensure your gas meter has credit if you use a pre-payment meter.Check outside to ensure the flue pipe is not blocked by debris or ice.Reset the boiler by turning the selector switch to 'OFF/RESET' and then back to 'ON'.
Your boiler has failed to light or stay lit, which is often caused by a blocked condensate pipe or a sensor detecting a problem with the ignition process.
Why it happens: This fault occurs when the boiler tries to ignite but fails to establish a steady flame, or if the safety sensors detect that the waste water cannot drain away properly. The most common reason is a blockage in the condensate trap or external pipework, which causes water to back up into the heat exchanger and extinguish the burner. It can also be triggered by worn ignition components that can no longer create a strong enough spark to light the gas.
Locate the external plastic condensate pipe and check if it has frozen in cold weather.If frozen, carefully pour warm (not boiling) water over the pipe to melt the ice.Restart the boiler by turning the mode selector switch to 'Reset' and then back to the original position.
Your boiler has shut down because its internal safety sensor has detected that the water temperature has risen too high.
Why it happens: This fault occurs when the water inside the heat exchanger reaches a dangerously high temperature, triggering a safety switch to prevent damage. The most common reasons are a pump failure that stops water from moving or a blockage in the system that prevents heat from escaping the boiler. It can also be caused by a faulty sensor sending an incorrect 'overheat' signal to the main control board.
Check that all radiator valves and boiler isolation valves are fully openTurn the selector switch to the 'OFF/RESET' position, wait five seconds, and turn it back to 'ON'Check that your system pressure is between 1 and 1.5 bar on the pressure gauge
Your boiler has sensed that the water returning from your radiators is too hot, which usually means the heat isn't being transferred out of the system properly.
Why it happens: This fault occurs when the water traveling back into the boiler is nearly as hot as the water leaving it, usually because the heat isn't being released into your rooms. The most common reasons are a pump failure that isn't moving the water fast enough, or a blockage in the system like trapped air or sludgy radiators that prevents proper circulation.
Check that all radiator valves (TRVs) are fully open and not stuck.Ensure the central heating bypass valve, if visible, is open.Check that the internal pump is audible and running.
Your boiler has shut down because it is getting too hot too quickly, usually because the water isn't moving through the system properly.
Why it happens: This fault occurs when the water inside your boiler heats up much faster than the system can carry it away, causing the unit to overheat for safety. The most common reason is a pump failure or a blockage in the pipes, which prevents the hot water from circulating around your radiators. It can also be caused by a build-up of sludge or debris that restricted the flow through the main heat exchanger.
Check that your radiator valves are open and not turned to zero.Ensure your system pressure is between 1.0 and 1.5 bar on the pressure gauge.Try resetting the boiler by turning the mode selector switch to 'OFF/RESET' for a few seconds.
Your boiler has shut down because a built-in safety sensor or an external monitoring device has detected a problem that prevents the system from running safely.
Why it happens: This fault occurs when an external safety component, such as a condensate pump or an overheat thermostat, sends a signal to the boiler to shut down for safety. The most common reason is that the condensate pump has failed or is full of water, triggering a cut-off switch to prevent a leak or internal damage. It can also be caused by a loose wire or a fault in the safety sensor itself.
Full guide for AL21on the Vokera Mynute Vhe
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 Vokera 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