BoilerFaultCodesThe 6 most common faults
Your boiler has detected that the water pressure in the system is too low to run safely and has stopped working to protect itself.
Locate the filling loop (usually a silver flexible hose) underneath or near the boiler.Slowly open the valve or valves on the filling loop until you hear water flowing.Watch the pressure gauge and close the valves tightly once the needle reaches between 1.0 and 1.5 bar.
Your boiler has experienced a lockout, meaning it has switched itself off for safety after failing to fire correctly.
Locate the reset button (labeled S1) on the control panel.Press and hold the reset button for a few seconds to see if the boiler restarts.If the boiler locks out again immediately, do not keep resetting it and call a professional.
Your boiler has stopped working safely and needs a simple restart to clear a temporary system error.
Locate the 'Reset' button (labeled S1) on the boiler control panel.Press and hold the Reset button for 2-3 seconds.Wait for the boiler to complete its startup sequence and check if the error light stops flashing.
Your boiler has stopped working because the water pressure inside the system has dropped too low to operate safely.
Check the pressure gauge; it is likely below 1.0 bar.Locate the filling loop (braided silver hose) usually under the boiler.Open the valves slowly to top up the water until the gauge reaches 1.5 bar.Close the valves tightly and press the S1 button on the boiler to reset the system.
Your boiler has switched itself off to prevent it from getting too hot and causing internal damage.
Wait for the boiler to cool down completelyLocate the S1 reset button on the control panelPress and hold the button to clear the fault and restart the unit
Your boiler has tried to start three times but hasn't been able to light the flame, so it has shut down for safety.
Check that your gas pre-payment meter (if you have one) has credit.Ensure your external gas emergency control valve is turned to the 'on' position.Press the central button (S1) beneath the boiler display to attempt a reset.
on the Gledhill GB35C
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 Gledhill 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