BoilerFaultCodesThe 6 most common faults
Your boiler has become too hot and has automatically shut itself down to prevent damage or safety issues.
Why it happens: This fault occurs when the water inside the heat exchanger reaches a dangerously high temperature, triggering a safety switch to cut the power. The most common reasons are a failed pump that isn't moving water away from the boiler quickly enough or a blockage in the system pipework. It can also happen if the internal sensors fail and wrongly report that the boiler is boiling over.
Locate the reset button on the front or underside of the boiler control panelPress the reset button firmly once to see if the red light goes out and the boiler restartsCheck that your radiator valves are open and that the pump is not making unusual grinding noises
Your boiler has detected an internal electrical or safety fault and has stopped running to prevent damage.
Why it happens: This fault occurs when the boiler's internal computer stops receiving signals from essential safety components or loses its electrical connection. It is usually caused by a loose wiring plug inside the unit or a component failing to complete an electrical circuit, which forces the boiler to shut down for safety. In some cases, fluctuations in your home's mains power supply can also trigger this red light.
Full guide for Red LED is 'ON'Your boiler has shut down because a safety sensor has detected that dangerous exhaust fumes are not escaping through the chimney correctly.
Why it happens: This fault occurs when a safety sensor detects that combustion gases are blowing back into the room instead of escaping through the chimney. The most common reasons are a blockage in the chimney, such as a bird's nest or debris, or severe atmospheric conditions preventing the natural flow of exhaust. The boiler shuts down immediately to prevent harmful carbon monoxide from entering your home.
Full guide for Red LED illuminated (Lockout)Your boiler has stopped working because it cannot light the internal flame, which means you currently have no heating or hot water.
Full guide for Flame Lock-outYour boiler has switched itself off because it became too hot, acting as a safety precaution to prevent damage.
Full guide for Red LED (Overheat)Your boiler has detected that fumes are not escaping properly through the flue, so it has shut itself down automatically to keep you safe from harmful exhaust gases.
Full guide for Red LED (TTB)on the Potterton Kingfisher MF RSL
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