BoilerFaultCodesThe 6 most common faults
Your boiler is unable to start because it cannot light the small pilot flame, meaning you will have no heating or hot water.
Why it happens: This fault occurs when the boiler attempts to start up but the small pilot flame fails to ignite or stay lit. The most common reasons include a blocked pilot burner caused by dust buildup, a worn-out sensor that can no longer detect the flame, or a fault within the gas valve preventing fuel from reaching the burner.
Check that your home's main gas emergency control valve is in the 'on' position.Verify if other gas appliances, like a cooker or hob, are working to confirm gas supply.If you have a prepaid gas meter, ensure you have sufficient credit and the meter hasn't locked out.
Your boiler's small pilot flame is not staying lit, which is preventing the main burner from starting up to provide heat.
Why it happens: This fault occurs when the small flame responsible for lighting the main burner fails to stay lit or cannot be detected by the system. The most common reasons include a worn-out heat sensor called a thermocouple, a blocked pilot hole preventing gas flow, or a buildup of soot on the sparking component. Without this steady pilot flame, the boiler shuts down as a safety precaution to prevent unburnt gas from escaping.
Locate the grey or white control knob on the boiler gas valve.Turn the knob to the 'Pilot' or 'Star' position and press it down firmly and completely.While holding the knob down, press the igniter button repeatedly until the pilot flame appears.Continue to hold the control knob down for 20-30 seconds after the flame is lit before slowly releasing it.
Your boiler is unable to start its pilot flame or has shut down to prevent the system from getting too hot.
Why it happens: This fault occurs when the boiler's internal safety sensors detect that the unit has become dangerously hot or when the pilot light fails to stay lit. The most common reason is a failing thermocouple that can no longer sense the flame, or a tripped overheat thermostat caused by a circulation issue like a pump failure.
Locate the overheat thermostat reset button, usually hidden under a small plastic cap on the front or bottom panel.Press the reset button firmly until you hear a click.Attempt to relight the pilot light following the instructions on the boiler's internal door.
Your boiler is failing to stay lit after you try to start it because the pilot light is going out as soon as you let go of the ignition button.
Why it happens: This fault occurs when the safety system, centered around a part called a thermocouple, fails to detect a stable flame. When you release the ignition button, the boiler shuts off gas flow because it incorrectly believes the pilot light has gone out, or the components responsible for holding the gas valve open have physically worn out. The most common reason is a deteriorated thermocouple tip that can no longer generate the tiny electrical pulse needed to keep the boiler running.
Locate the gas control knob on the boiler.Follow the lighting instructions on the boiler casing, ensuring you press the control knob in fully.Hold the control knob down for at least 20 to 30 seconds after the pilot flame appears before slowly releasing it.
Your boiler's pilot light is on, but the main burner is not firing up because your external heating controls are not telling the boiler to start.
Why it happens: This issue occurs because the boiler is waiting for a signal from your external equipment that never arrives. Even though the boiler is ready to work, the wall thermostat, timer, or a motorised valve in your airing cupboard has likely failed or reached its target temperature and isn't sending the 'start' command. It means the boiler itself is often healthy, but the system's brain or its switching components have lost communication.
Check that your wall thermostat is turned up higher than the current room temperature.Ensure your programmer or heating timer is set to 'On' or 'Auto'.Check if the batteries in your wireless thermostat need replacing.
Your boiler is unable to start because the small starter flame is not lighting, likely due to a tiny blockage in the gas supply line.
Why it happens: This fault occurs when the tiny orifice in the pilot injector becomes restricted by microscopic debris or carbon buildup, preventing the starter flame from reaching the sensor. Without this stable pilot flame, the boiler’s safety system refuses to open the main gas valve to prevent unburned gas from escaping. The most common reason is simply age-related wear or dust being drawn into the pilot assembly over time.
Full guide for A.(3)on the Potterton Kingfisher 2 RS60, RS80, RS100
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