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 has stopped working because the water pressure inside the system has dropped too low to operate safely.
Why it happens: This fault occurs when the boiler's internal electronics detect a brief interruption or a glitch in the data being sent between sensors. The most common cause is a sensor that is starting to wear out or a small electrical disturbance on the main control board that makes the system pause to re-check its readings.
Locate the filling loop, which is a silver braided hose with one or two small valves under the boiler.Open the valves slowly to allow water into the system until the pressure gauge on the front of the boiler reaches 1.5 bar.Close the valves firmly and check the gauge to ensure it stays stable.
Your boiler has detected an internal communication or temperature sensor error that is currently preventing it from running normally.
Why it happens: This fault occurs when the boiler's control board fails to receive a consistent signal from the internal temperature sensors. The most common reason is a malfunctioning sensor that provides an incorrect reading, though it can also be caused by a loose wiring connection or a developing fault on the main circuit board.
Turn the mode selector switch to the 'OFF/RESET' position.Wait for approximately 30 seconds.Turn the switch back to the 'ON' or heating/hot water position.
Your boiler has detected a temporary internal communication error or a sensor synchronization issue that is preventing it from running properly.
Why it happens: This fault occurs when the boiler's internal control board loses track of the temperature readings because the signals from the sensors are inconsistent or mismatched. It is often caused by a failing hot water sensor sending incorrect data or a minor electronic glitch on the main circuit board that prevents the components from communicating correctly.
Turn the selector switch to the 'OFF/RESET' position.Wait for approximately 30 seconds.Turn the selector switch back to the 'ON' position (Heating and Hot Water icon).
on the Vokera Syntesi 25
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