BoilerFaultCodesThe 6 most common faults
Your boiler has tried to light several times without success, meaning your heating and hot water will not work until the gas supply is restored or the ignition is fixed.
Check that your gas emergency control valve is in the 'on' positionCheck if other gas appliances (like a hob) are working to confirm gas flow to the propertyIf you have a prepaid gas meter, ensure it has sufficient creditGently press the reset button on the control panel to see if the boiler restarts
Your boiler has become too hot and has shut down as a safety precaution to prevent damage.
Check that your radiator valves and any isolation valves are fully openBleed your radiators to remove any trapped airEnsure the system pressure is between 1.0 and 1.5 barPress the reset button to restart the boiler
Your boiler is struggling to detect or maintain the correct amount of water inside the system.
Check the pressure gauge on the front of the boiler; it should be between 1.0 and 1.5 bar.If the pressure is too low, use the external filling loop valves to top up the system water.Ensure any isolation valves under the boiler are fully open and restart the unit.
Your boiler has shut down because it keeps losing water pressure and needs a manual reset and top-up.
Check the pressure gauge; it should be between 1.0 and 1.5 barLocate the external filling loop and top up the water pressureInspect radiators and pipework for visible signs of a leakPress the 'Reset' button on the boiler control panel
Your boiler has started an ignition sequence but the flame went out, likely due to a blocked pipe or an issue with the gas supply.
Check the white plastic condensate drain pipe outside for any signs of freezing or blockages.Inspect the flue terminal on your outside wall to ensure no debris, nests, or snow are blocking the air flow.If you use LPG, check that your tank has not run out of fuel.Press the 'Reset' button on the boiler control panel.
Your boiler has detected that the electrical power coming from your mains supply is too low for it to operate safely.
Check if other appliances in your home are flickering or behaving strangelyCheck your consumer unit (fuse box) to ensure no switches have trippedContact your electricity network provider to see if there is a known power fluctuation or brownout in your area
on the Keston Celsius 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 Keston 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