BoilerFaultCodesThe 6 most common faults
Your boiler has shut down because it has detected an unsafe increase in temperature and has triggered a safety cut-out to prevent damage.
Why it happens: This fault occurs when the water inside the boiler reaches an unsafe temperature, forcing a safety switch to trip and shut the system down. The most common reasons are a lack of water flow caused by a failing pump, a blockage in the pipework, or a buildup of air within the heat exchanger.
Check that your radiator valves and any zone valves are fully open to allow water to circulate.Ensure your system pressure is topped up to between 1 and 1.5 bar.Allow the boiler to cool down completely, then press and hold the 'Reset' button for five seconds.
Your boiler has detected that the water pressure is too low for it to run safely and has shut down as a precaution.
Why it happens: This fault occurs when the internal sensor detects that there is not enough water inside the central heating system to operate safely. The most common reason is a gradual loss of pressure through a small leak on a radiator valve or because the system was recently bled without being topped up.
Locate the external filling loop, which is usually a silver flexible hose underneath the boiler.Open the small black valves at either end of the hose to allow water into the system.Monitor the pressure gauge on the front of the boiler until it reaches between 1 and 1.5 bar.Close both valves tightly and press the 'Reset' button on the boiler control panel.
Your boiler has failed to light because it either cannot get enough gas or cannot detect a flame once ignited.
Why it happens: This fault occurs when the boiler attempts to ignite but cannot establish or maintain a steady flame. The most common reasons include a lack of gas reaching the burner, a faulty ignition spark, or a sensor that is too dirty to detect that the flame has successfully lit.
Check that your gas emergency control valve is open and any prepay gas meter has credit.If it is freezing outside, check that the white plastic condensate pipe leading outdoors is not frozen and blocked.Hold the 'Reset' button for five seconds to attempt to restart the boiler.
Your boiler has sensed that water is not circulating properly before it starts the heating process, which is usually caused by an air lock or a blockage.
Why it happens: This fault occurs when the boiler's internal sensors detect that water isn't moving through the unit quickly enough during its initial checks. This is usually caused by a large pocket of air trapped inside the pipework or a failing pump that no longer has the power to push water around the system. In some cases, a build-up of sludge or debris can also create a physical blockage that restricts the flow.
Check that your system pressure is between 1 and 1.5 bar on the pressure gaugeEnsure all radiator valves and isolation valves under the boiler are fully openGently bleed your radiators to remove any trapped air
Your boiler has lost its connection to the sensor that monitors the temperature of the water in your heating system, causing the boiler to stop working.
Why it happens: This fault occurs when the boiler's control board can no longer read the temperature of the water leaving the unit. The most common cause is a failed internal sensor that has either burnt out or developed an electrical fault, though it can also be triggered by a loose or damaged connection in the internal wiring.
Full guide for E20Your boiler has detected a problem with the sensor that monitors the temperature of the exhaust gases, causing it to stop running for safety.
Why it happens: This fault occurs when the sensor responsible for monitoring the temperature of the exhaust gases sends an incorrect or missing signal to the boiler's internal computer. The most common reason is that the sensor itself has worn out or developed a short circuit, though loose or damaged wiring between the sensor and the main control board can also trigger the shutdown.
Full guide for E28on the Potterton Promax System HE Plus
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