BoilerFaultCodesThe 6 most common faults
Your boiler has completely lost its electrical supply and is showing no lights at all on the front display.
Check that the fused spur switch supplying the boiler is switched on.Go to your home's main electrical consumer unit (fuse box) to check if a circuit breaker has tripped.Check if other appliances nearby have power to rule out a general house power cut.
Your boiler has lost its power supply or the internal fuse has blown, meaning the unit is completely switched off.
Check that the fused spur switch supplying the boiler is turned on.Check your home's main fuse box (consumer unit) to ensure the circuit breaker for the boiler has not tripped.If the breaker has tripped, try resetting it once. If it trips again immediately, do not attempt further resets.
Your boiler is currently switched on and ready to work, but it is not starting up because your thermostat or timer is not sending a signal for heat.
Check that your room thermostat or smart controller is set to a temperature higher than the current room temperature.Check the batteries in your wireless room thermostat and replace them if they are flat.Ensure your heating timer or programmer is currently scheduled to be in an 'On' period.
Your boiler has stopped working because the water pressure inside the system has dropped too low.
Locate the filling loop valves underneath your boiler.Open the valves gently to let water into the system until the pressure gauge reads between 1 and 1.5 bar.Close both valves tightly and reset the boiler.
Your boiler has stopped working because it has detected that the water pressure inside the system is too low.
Locate the filling loop flexible hose underneath your boiler.Open the valves slowly to let mains water into the heating system.Watch the pressure gauge until it reaches between 1.0 and 1.5 bar, then firmly close the valves.
Your boiler has lit correctly but the flame has gone out unexpectedly, causing the system to shut down for safety.
Check if other gas appliances like your oven or hob are working to ensure gas is reaching the propertyCheck if your gas meter has credit (if using a pre-payment meter)Reset the boiler by pressing the reset button for five seconds
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