BoilerFaultCodesThe 6 most common faults
Your boiler has shut down because it has detected it is getting too hot, usually caused by a circulation problem or a blockage.
Why it happens: This fault occurs when the internal safety sensors detect that the water inside the boiler has reached an unsafe temperature, triggering an automatic shutdown to prevent damage. The most common reasons are a pump failure that stops water from moving or a buildup of sludge and debris that creates a blockage in the heat exchanger.
Check that your radiator valves are openEnsure there is enough water pressure in the system (usually between 1 and 1.5 bar)Wait for the boiler to cool down and try pressing the reset button
Your boiler has stopped working because the water pressure is too low and needs to be topped up.
Why it happens: This fault occurs when the water pressure inside your central heating system drops below the minimum level required for the boiler to operate safely. The most common reason is a tiny leak in the pipework or radiators, though it can also happen if you have recently bled your radiators and haven't topped the pressure back up.
Locate the filling loop (usually a silver flexible hose) underneath your boiler.Slowly open the one or two taps/valves until you hear water entering the system.Watch the pressure gauge and close the taps once the needle reaches between 1 and 1.5 bar.
Your boiler is struggling to move water around the system effectively, which is causing it to shut down to prevent overheating.
Why it happens: This fault occurs when the boiler detects that water is not moving through the internal pipework quickly enough to carry heat away from the burner. The most common reasons are a failed internal pump, a blockage caused by system sludge, or a valve that has become stuck and is blocking the flow. Because the heat cannot escape, the boiler shuts down immediately to protect its internal components from melting or cracking.
Check that your radiator valves are fully openEnsure your boiler pressure is between 1.0 and 1.5 bar on the gaugeGently bleed your radiators to remove any trapped air pockets
Your boiler has failed to light because it either cannot get enough gas or it cannot detect the flame it has sparked.
Why it happens: This fault occurs when the boiler attempts to ignite but fails to establish or maintain a stable flame. The most common reasons are a temporary interruption in the gas supply, a blocked burner, or an ignition probe that has become worn and can no longer sense the heat from the flame.
Check that your gas stopcock is fully open and your gas meter has credit.Try turning on another gas appliance, like a hob, to see if the gas supply is active.Press the 'Reset' button on the front of the boiler for five seconds.
Your boiler's internal temperature sensor has stopped sending a reliable signal, which means the system cannot safely monitor how hot the water is for your radiators.
Why it happens: This fault occurs when the thermistor, a small sensor that monitors water temperature, fails or provides an incorrect electrical reading to the boiler's control board. The most common reason is internal degradation over time or loose wiring connections, which prevents the boiler from knowing when to safely turn the burner on or off.
Full guide for E20Your boiler's internal sensor that monitors exhaust gases has developed a fault, causing the system to shut down for safety.
Why it happens: This fault occurs when the boiler's internal safety sensor detects that the exhaust gases are too hot or if the sensor itself has suffered an electrical failure. Over time, the sensor can degrade due to constant exposure to heat, or the wiring connecting it to the main control board may have become loose or damaged. Because this component monitors high temperatures, the boiler shuts down immediately to prevent any internal damage.
Full guide for E28on the Potterton Gold HE
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 Potterton 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