BoilerFaultCodesThe 6 most common faults
Your boiler has tried to start up but cannot light the gas flame, which means your heating and hot water will not work.
Why it happens: This fault occurs when the boiler's control system attempts to light a flame but fails to detect one after several attempts. The most common reasons include a lack of gas reaching the burner, a worn-out spark electrode that cannot create a spark, or a faulty internal component failing to signal that the gas is lit.
Check that your gas pre-payment meter has creditEnsure the gas stopcock is fully open and other gas appliances like the hob are workingPress and hold the reset button for five seconds
Your boiler has detected that there is not enough water in the system to operate safely, causing it to shut down temporarily.
Why it happens: This fault occurs when the internal sensor detects that the system's water pressure has dropped too low for the boiler to operate safely. The most common reason is a slow leak in the pipework or radiators, though it can also happen if you have recently bled your radiators without topping the water back up.
Locate the filling loop (the flexible silver hose) underneath your boiler.Slowly open the valve(s) to allow water into the system while watching the pressure gauge.Close the valves tightly once the gauge reaches between 1.0 and 1.5 bar.Press the reset button on the boiler control panel.
Your boiler is trying to start up but cannot light the gas to create a flame, meaning you will have no heating or hot water.
Why it happens: This fault occurs when the boiler's control system attempts to light the burner but fails to detect a stable flame after several attempts. The most common reasons are a lack of gas reaching the unit, worn-out spark electrodes that can no longer create an ignition, or a faulty internal component failing to send the 'start' signal.
Check if other gas appliances, like a hob, are working to confirm gas supplyVerify that your prepaid gas meter (if applicable) has creditPress the reset button or turn the control knob to 'Reset' for 2 seconds
Your boiler has tried to start up but failed to ignite the gas flame, causing the system to shut down for safety.
Why it happens: This fault occurs when the boiler's internal computer tries to start the combustion process but cannot detect a stable flame within the safety timeframe. It is often caused by a lack of gas reaching the burner, a build-up of carbon on the spark electrodes, or a worn-out sensor that can no longer 'see' the flame even if it has lit.
Check that your gas prepay meter has creditEnsure other gas appliances in your home (like a hob) are workingPress the reset button once to see if the boiler restarts
Your boiler has detected a problem with how it moves air and exhaust gases through the system, preventing it from firing up safely.
Why it happens: This fault occurs when the boiler's internal safety sensor cannot confirm that the fan is successfully pushing exhaust gases out of the flue. The most common reasons are a build-up of debris in the small plastic tubes inside the unit or a mechanical failure in the fan or air pressure sensor. Without this confirmation, the boiler refuses to light the gas burner to prevent dangerous fumes from backing up into your home.
Full guide for LED1 on, LED2 flashingYour boiler has detected a problem with the sensor that monitors the temperature of your central heating water, meaning it can't heat your radiators safely.
Why it happens: This fault occurs when the internal sensor responsible for tracking the temperature of your radiators fails to send a reliable signal to the boiler's control board. The most common reason is that the sensor has physically degraded over time or the electrical connection has become loose, preventing the boiler from knowing when to safely turn the burner on or off.
Full guide for LED1 flashing, LED2 onon the Ideal Mini S18
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