BoilerFaultCodesThe most common Main faults
Your boiler is struggling to move water around the system before it starts the heating process, which is often caused by a blockage or a pump issue.
Why it happens: This fault occurs when the boiler detects that water isn't moving through the unit quickly enough during its initial startup checks. The most common reasons are a build-up of sludge blocking the internal pipework or a mechanical failure of the pump that circulates the water. Because the water can't flow, the boiler shuts down to prevent the heat exchanger from overheating.
Check that your boiler pressure is between 1.0 and 1.5 bar on the pressure gaugeEnsure all radiator valves and boiler isolation valves are fully openGently bleed your radiators to remove any trapped air pockets
Your boiler has switched itself off because it has reached an unsafe temperature, usually due to a lack of water flow or a circulation problem.
Why it happens: This fault occurs when the water inside the boiler gets too hot, triggering a safety switch to prevent damage. The most common reasons are a pump failure that stops water from moving or a blockage in the system pipes that traps heat inside the heat exchanger.
Check if your radiator valves are openCheck the boiler pressure gauge and top up to 1.5 bar if lowPress the 'R' or 'Reset' button for 2 seconds once the boiler has cooled down
Your boiler has stopped working because the water pressure in the system has dropped too low and needs topping up.
Why it happens: This fault occurs when the pressure within your central heating system drops below a safe operating level, usually because water has escaped the circuit. The most common reasons for this are a leak in the radiator valves or pipework, or air being released from the system through recent bleeding of the radiators.
Locate the filling loop (usually two braided silver hoses or blue levers) underneath the boiler.Open the valves slowly until you hear water entering the system.Watch the pressure gauge and close the valves tightly once the needle reaches 1.5 bar.
Your boiler is struggling to move hot water around the system, which is usually caused by a blockage or a pump issue that is preventing the unit from cooling itself down.
Why it happens: This fault occurs when the boiler detects that water is not moving through the system quickly enough to carry heat away from the burner. The most common reasons are a failed internal pump that can no longer push the water, or a build-up of debris and sludge that has physically blocked the pipes or heat exchanger. Effectively, the boiler shuts down because it is getting too hot too quickly and needs to prevent internal damage.
Check that all radiator valves are fully openEnsure the boiler pressure is between 1.0 and 1.5 bar on the gaugeGently bleed air from your radiators using a radiator key
Your boiler has lost its flame while running, which means it has safely shut down to prevent issues.
Why it happens: This fault occurs when the boiler's control system loses the signal that a flame is present while it should be firing. It is often caused by a buildup of carbon on the electrodes or a blockage in the condensate trap that backs up and 'drowns' the flame. In some cases, it can also be triggered by an inconsistent gas supply or a failing gas valve that cannot maintain a steady flow.
Check if other gas appliances, like a hob, are working to confirm gas supplyEnsure your pre-pay gas meter has sufficient creditPress and hold the Reset button for five seconds
Your boiler has failed to light because it is not receiving enough gas or cannot detect the flame used to heat your water.
Why it happens: This fault occurs when your boiler tries to light itself several times but fails to establish or maintain a steady flame. The most common reason is a shortage of gas reaching the burner, often caused by an external supply issue or a blockage in the internal components. It can also happen if the sensor that monitors the flame is dirty or damaged, preventing the boiler from knowing it has successfully fired up.
Check if other gas appliances, like a cooker hob, are working to confirm your gas supply is active.If you have a prepayment meter, check that you have enough credit.Locate the white pipe beneath the boiler and ensure it hasn't frozen if the weather is very cold.Press the 'Reset' button for five seconds to see if the boiler restarts.
Your boiler has lost its gas supply, meaning it cannot light the flame to provide heating or hot water.
Why it happens: This fault occurs when the boiler's internal safety sensors detect that gas is not reaching the burner or the flame isn't staying lit. It is often caused by a closed gas meter valve, a blockage in the supply pipe, or a mechanical failure of the gas valve within the unit itself. In some cases, the boiler may simply have air trapped in the system after a period of non-use or a recent gas works.
Check that your gas emergency control valve (usually by the meter) is in the 'on' position.If you have a pre-payment meter, check that you have sufficient credit and the valve hasn't closed.Check if other gas appliances, like a hob, are working to confirm if the issue is with the boiler or the whole house supply.Try resetting the boiler by turning the selector switch to the 'R' position for at least five seconds.
Your boiler has detected that water is not moving through the system correctly, causing it to overheat quickly.
Why it happens: This fault occurs when the water inside your boiler heats up too quickly because it isn't being moved away into your radiators or hot water tank. The most common reasons are a pump that has seized up, a build-up of sludge blocking the pipework, or air trapped within the system preventing flow.
Check that your boiler pressure is between 1 and 1.5 bar on the gauge.Ensure all radiator valves and isolation valves under the boiler are fully open.Gently bleed your radiators to remove any trapped air pockets.Reset the boiler to see if the fault clears.