BoilerFaultCodes
The most common Keston 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 has become too hot and has shut itself down as a safety precaution to prevent damage.
Why it happens: This fault occurs when the water inside the heat exchanger reaches a dangerously high temperature, triggering a safety sensor to cut the power. The most common reasons are a lack of water flow caused by a failed pump, a blockage in the pipework, or air trapped within the system preventing heat from being moved away from the burner.
Check that the boiler pressure is between 1.0 and 1.5 bar on the gauge.Ensure all radiator valves and internal isolation valves are fully open.Bleed your radiators to remove any trapped air pockets from the system.
Your boiler has stopped working because it cannot correctly detect the water pressure, often due to a low water level or a faulty sensor.
Why it happens: This fault occurs when the boiler's internal computer is unable to detect a stable reading from the water pressure sensor, which is essential for safe operation. The most common reason is that the system water level has dropped too low, but it can also be triggered if the sensor itself has become blocked with debris or has failed electronically.
Check the pressure gauge on the front of the boilerIf the pressure is below 1 bar, use the filling loop to top it up to 1.5 barReset the boiler by pressing the 'Reset' button
Your boiler has shut down because it keeps losing water pressure and likely has a leak somewhere in the heating system or the unit itself.
Why it happens: This fault occurs because the boiler has detected a significant and repetitive drop in water pressure, forcing it to shut down to prevent internal damage. It is usually caused by a physical leak within your radiators, pipework, or the boiler's internal components, such as a failing pressure relief valve. If the system cannot maintain a steady pressure four times within a single day, the software triggers this safety lock to alert you to the underlying leak.
Check for visible water leaks under the boiler and around your radiators or valves.Top up the system pressure to 1.5 bar using the external filling loop.Reset the boiler and monitor if the pressure drops again.
Your boiler is struggling to keep its flame lit, which often happens because the drainage pipe is blocked or frozen, or there is an issue with the air supply.
Why it happens: This fault occurs when the boiler's internal computer detects that the flame has unexpectedly gone out during operation. The most common reason is that waste water cannot escape the unit due to a blockage in the drainage pipe, which causes the system to flood and extinguish the burner. It can also be caused by a lack of fresh air reaching the boiler or an unstable gas supply preventing a consistent flame.
Check the white plastic condensate pipe outside for signs of ice or blockages.If frozen, gently pour warm (not boiling) water over the pipe to thaw it.Ensure the external flue terminal is not obstructed by debris or garden foliage.