BoilerFaultCodesThe 6 most common faults
Your boiler is unable to light the flame needed to heat your water and radiators, often due to a temporary interruption in the gas supply.
Why it happens: This fault occurs when the boiler tries to start up but cannot successfully create or see a flame at the burner. The most common reasons are a temporary interruption in your gas supply, a build-up of dirt on the ignition probes, or a component failure that prevents the gas from flowing correctly. Essentially, the safety system has stepped in because it cannot confirm that the fuel is burning safely.
Check if other gas appliances, like a cooker, are working to confirm gas is reaching the property.Ensure your gas meter has credit if you use a pre-payment meter.Press the reset button on the boiler control panel and hold for a few seconds to try and restart the ignition sequence.
Your boiler has reached an unsafe temperature because the water is not circulating correctly through the system.
Why it happens: This fault occurs when the water inside the boiler gets too hot because it cannot flow away from the heat source quickly enough. The most common reasons are a pump that has seized up or internal valves being accidentally left closed, which traps the heat and triggers a safety shutdown.
Check that the isolation valves under the boiler are in the open positionEnsure all radiator valves (TRVs) are turned up to fullTry resetting the boiler using the control knob to see if the pump clears the blockage
Your boiler has detected that the water pressure is too low to operate safely, which is usually caused by a leak or air trapped in the system.
Why it happens: This fault occurs when the internal sensors detect that the water level inside your central heating system has dropped below a safe threshold. The most common reason is a slow leak from a pipe or radiator, though sometimes the pressure drops simply because air has escaped through the system's vent.
Locate the filling loop (a flexible silver hose) underneath the boiler.Slowly open the one or two taps on the hose until you hear water flowing.Watch the pressure gauge and close the taps once the needle reaches between 1.0 and 1.5 bar.
Your boiler's waste water pipe is blocked or frozen, preventing the system from draining properly and causing it to shut down for safety.
Why it happens: This fault occurs when the liquid produced by the boiler during operation cannot flow away, causing it to back up into the system. The most common reason is a blockage in the drainage pipe, often caused by a buildup of debris in the internal trap or ice forming in the external pipework.
Locate the plastic pipe leading from the boiler to the outside drain.Check if the pipe is frozen and gently pour warm (not boiling) water over it to thaw.Ensure the internal trap or collection bottle is not full of debris.Reset the boiler once the blockage is cleared.
Your boiler has stopped working because the pipe that lets exhaust gases out is blocked or the internal sensor that checks for airflow is clogged with dirt.
Why it happens: This fault occurs when the boiler's safety sensors detect that harmful exhaust gases are not being cleared from the system correctly. The most common cause is a buildup of dust or debris inside the small tubes that monitor airflow, or a mechanical failure in the fan that pushes the gases outside.
Full guide for 03Your boiler is having trouble 'talking' to your wall-mounted thermostat or remote control unit.
Why it happens: This fault occurs when the digital handshake between the boiler's internal computer and the wall-mounted controller is broken. The most common reason is a loose or damaged connection in the low-voltage wiring that links the two components, though it can also be caused by an internal electronic failure within the remote control unit itself.
Full guide for 05on the Vokera Syntesi 29
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