BoilerFaultCodesThe 6 most common faults
Your boiler has stopped working because the water pressure inside the system has dropped too low to allow it to run safely.
Why it happens: This fault occurs when the water level inside your central heating system drops below the minimum required for the boiler to operate. The most common reasons are a slow leak from a radiator valve or pipework, or the air pressure inside the expansion vessel needs recharging. In some cases, it can also happen after you have recently bled your radiators, which removes air but also lowers the overall system pressure.
Locate the filling loop (usually a silver flexible hose) underneath the boiler.Slowly open the one or two small valves on the ends of the pipe until you hear water flowing.Watch the pressure gauge and close the valves tightly once the needle reaches between 1 and 1.5 bar.
Your boiler has failed to ignite, which means it cannot provide heat or hot water because it isn't successfully lighting a flame.
Why it happens: This fault occurs when the boiler's control system attempts to start a flame but fails to detect one after several attempts. The most common reasons include a lack of gas reaching the unit, a worn-out ignition spark, or a blockage in the pipes that carry exhaust fumes away from your home.
Check if other gas appliances, like a cooker hob, are working to confirm gas supply.Check that your gas meter has credit if you have a pre-payment meter.Reset the boiler by turning the mode selector switch to the 'Reset' position for a few seconds and then back to 'On'.
Your boiler has failed to light because either the gas didn't ignite or a sensor has detected that the condensate drainage pipe is blocked.
Why it happens: This fault occurs when the boiler attempts to start but cannot safely confirm a flame is present. The most common reasons are that the gas supply isn't reaching the burner, the ignition electrodes are worn out, or the internal drainage pipe is backed up with water, which triggers a safety sensor to prevent an overflow.
Check if your gas supply is active (e.g. check other gas appliances or your prepayment meter balance).Inspect the white plastic pipe leading outside for ice or blockages; if frozen, gently defrost it with warm (not boiling) water.Turn the mode selector dial to the 'RESET' position for a few seconds, then back to your desired setting.
Your boiler has sensed that it is starting to overheat and has shut itself down as a safety precaution.
Why it happens: This fault occurs when the temperature inside the boiler exceeds a safe limit, causing a safety sensor to trip and shut the system down. The most common reasons are a pump failure that prevents hot water from moving away from the burner, or a build-up of sludge and limescale that restricts flow through the heat exchanger.
Turn the mode selector switch to the OFF/RESET position, wait a few seconds, then move it back to the 'Hot Water' or 'Heating' position.Check that your radiator valves are open and not blocked by furniture.Ensure there is enough pressure in the system by checking the gauge is between 1 and 1.5 bar.
Your boiler has shut down because the water returning to the unit is too hot, which usually means heat isn't being distributed around your home properly.
Why it happens: This fault occurs when the water coming back into the boiler is too hot, causing the system to shut down for safety. It usually means the heat cannot escape the boiler, often due to a pump failure that isn't moving the water or a blockage in the pipework. Sometimes, a faulty sensor incorrectly reports a high temperature even when the water is cool.
Check that all radiator valves (TRVs) are fully openEnsure the boiler pressure gauge is between 1.0 and 1.5 barReset the boiler by turning the mode selector dial to 'OFF/RESET' and back to 'ON'
Your boiler has detected that the water pressure in the central heating system is too low to operate safely and has shut down.
Why it happens: This fault occurs when the internal sensor detects that there isn't enough water pressure to safely circulate heat around your home. The most common reason is a slow leak somewhere in the radiator network or a drop in pressure following the bleeding of your radiators. In some cases, a component inside the boiler like the expansion vessel may have lost its charge, leaving the system unable to maintain steady levels.
Locate the external filling loop, which is usually a flexible silver hose with one or two black taps underneath the boiler.Slowly open both taps (or one if there is only one) until you hear water flowing into the boiler.Watch the pressure gauge on the front of the boiler and close the taps once the needle reaches between 1.0 and 1.5 bar.Press the Reset button on the boiler control panel to clear the fault code.
on the Vokera Unica 24HE
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