BoilerFaultCodesThe 6 most common faults
Your boiler has detected that the water pressure in the system is too low, causing it to stop running for safety.
Why it happens: This fault occurs when the water levels inside your heating system drop below the minimum required for the boiler to operate safely. The most common reasons for this are a leak somewhere in the pipework or radiators, or simply that air was recently bled from the system without topping the pressure back up.
Locate the filling loop, which is usually a flexible silver hose under the boiler.Slowly open the small tap (or taps) on the filling loop until you hear water moving.Watch the pressure gauge and close the taps exactly when the needle reaches 1.5 bar.
Your boiler has shut down because the water inside it has become too hot, likely due to a circulation problem.
Why it happens: This fault occurs when the water leaving your boiler exceeds a safe temperature limit, causing the system to shut down for safety. It is typically caused by a blockage in the pipework, a failing pump that cannot move the water quickly enough, or a build-up of debris known as sludge.
Check that your radiator valves are fully open to allow water to flow.Ensure your system pressure is between 1.0 and 1.5 bar on the pressure gauge.Press the 'Reset' button on the boiler control panel once the unit has cooled down.
Your boiler has lost its flame signal during operation, meaning and it can no longer safely heat your water or radiators.
Why it happens: This fault occurs when the boiler's internal sensor can no longer detect a steady flame while the system is running. The most common reasons include a buildup of carbon on the sensing probe, a failing gas valve that isn't providing enough fuel, or an unstable electrical signal that causes the safety system to shut the boiler down.
Check that your gas emergency control valve is in the 'on' position and you have credit on your gas meter.Inspect the outdoor condensate pipe for signs of freezing or blockages if the weather is very cold.Press the Reset button for two seconds to see if the system reignites.
Your boiler has lit correctly but the flame has gone out unexpectedly, often due to a fuel supply issue or a blockage in the condensate pipe.
Why it happens: This fault occurs when the boiler successfully ignites but cannot maintain a steady flame, causing the system to shut down for safety. The most common reasons include a temporary interruption in the gas supply, a dirty internal sensor that can no longer 'see' the flame, or a blockage in the drainage pipe that causes water to back up into the heat exchanger.
Check that your gas emergency control valve is open and you have credit on your meter.Check if the condensate discharge pipe (the plastic pipe leading outside) is frozen or blocked.Reset the boiler by pressing the 'Restart' button.
Your boiler's main control computer is missing a vital activation chip, which means the system cannot start up or provide any heat.
Why it happens: This fault occurs when the boiler's main control board cannot detect the unique memory chip that tells it how to operate safely. The most common reason is that the chip card has vibrated loose, failed electronically, or was not correctly transferred when a technician replaced the circuit board.
Full guide for F0Your boiler has detected that the electricity supply coming into your home is at a lower voltage than it needs to operate safely.
Why it happens: This fault occurs when the boiler's internal sensors detect that the incoming electrical voltage from your mains supply has dropped below the minimum level required for the components to function. Most commonly, this is caused by a temporary fluctuation in the local power grid, though it can also indicate a failing printed circuit board (PCB) that can no longer process power correctly.
Full guide for F7on the Keston S30
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 Keston 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