BoilerFaultCodesThe 6 most common faults
Your boiler is not receiving enough gas to stay lit safely, which is preventing your heating and hot water from working.
Why it happens: This fault occurs when the incoming gas pressure drops below the minimum level required for the boiler to operate safely. The most common reasons are a blockage in the gas supply line, a failing gas valve within the boiler, or an issue with the external regulator on your gas meter.
Check that your gas emergency control valve (usually by the meter) is fully openIf you have a pre-payment meter, check that you have sufficient credit and the valve hasn't trippedCheck if other gas appliances in your home, like a hob, are working correctly to rule out a grid supply issue
Your boiler has detected that water is moving too slowly or not at all through the system, causing a heat imbalance that has triggered a safety shutdown.
Why it happens: This fault occurs when the boiler's internal sensors detect that the outgoing water is significantly hotter than the returning water, suggesting a lack of circulation. The most common reason is a failed or stuck pump, though it can also be triggered by air trapped in the system or a blockage in the pipework. In some cases, a build-up of sludge or debris within the heat exchanger prevents the water from moving through the boiler fast enough to carry the heat away.
Check that your central heating valves and all radiator valves are fully openEnsure there is no air trapped in the system by bleeding your radiatorsCheck if the system pressure gauge is between 1 and 1.5 bar
Your boiler has shut down because it believes the internal water pressure is too low or it is getting too hot inside.
Why it happens: This fault occurs when the boiler's safety sensors detect that there isn't enough water pressure to operate safely or that the internal exhaust gases are reaching dangerous temperatures. It is often caused by a leak in the system, a failing pressure sensor, or an internal component like the expansion vessel losing its air charge. When these conditions are met, the boiler shuts down immediately to prevent serious damage to the heat exchanger.
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 to see if the error clears
Your boiler has shut down because the water inside it has become too hot, which is often caused by a blockage or a pump that isn't moving water through the system correctly.
Why it happens: This fault occurs when the water inside the boiler exceeds a safe temperature limit, causing the system to shut down for safety. The most common reasons are a failed pump that isn't circulating the water, or a physical blockage like limescale or sludge that is stopping the heat from escaping the boiler.
Check that all radiator valves and boiler isolation valves are fully openCheck your system pressure gauge is between 1 and 1.5 barOnce the boiler has cooled down, attempt to reset it using the reset button
Your boiler has switched itself off because the water returning to the unit is too hot, meaning the heat isn't being distributed around your home properly.
Why it happens: This fault occurs when the water returning to the boiler is almost as hot as the water leaving it, indicating that heat is not being transferred into your radiators or cylinder. The most common reason is a failure of the external pump or a blockage in the pipework that prevents the water from circulating through your heating system. It can also be caused by all your radiator valves being closed at the same time, leaving the hot water with nowhere to go.
Ensure all radiator valves (TRVs) are fully open to allow water to circulateCheck that your external pump (if applicable) is running and hasn't seizedInspect the system's bypass valve to ensure it isn't closed or blocked
Your boiler is heating up too quickly and has shut down to prevent overheating, likely because the water isn't moving through the system properly.
Why it happens: This fault occurs when the water inside the heat exchanger reaches its maximum safe temperature almost immediately after the burner ignites. The most common reason is a blockage or a failed pump preventing water from circulating, which causes the stationary water to boil instantly. It can also be triggered by a faulty sensor sending incorrect temperature readings to the boiler's control board.
Check that all radiator valves are fully openEnsure the boiler pressure is between 1.0 and 1.5 bar on the gaugeCheck if the secondary heating pump is running or if there is a blockage in the external pipework
on the Ideal Ideal Classic SE15P FF
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 Ideal 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