BoilerFaultCodesThe 5 most common faults
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 onYour boiler has detected a sensor problem that is preventing it from providing hot water correctly.
Why it happens: This fault occurs when the sensor responsible for measuring the temperature of your hot water fails to provide a consistent reading to the boiler's control board. The most common reason is that the internal components of the sensor have degraded over time, though it can also be triggered by a loose or damaged connection in the electrical wiring. As a safety precaution, the boiler stops heating water to prevent it from becoming dangerously hot or staying stone cold.
Full guide for LED2 flashing, LED3 onYour boiler has detected a minor electronic sensor issue and is running at a lower power level to keep your home warm until it can be serviced.
Why it happens: This fault occurs when one of the internal temperature sensors sends an inconsistent signal to the main control board, suggesting the sensor is starting to fail or has a poor electrical connection. Instead of shutting down completely, the boiler enters a safety mode to prevent overheating while still providing basic heating. The root cause is typically wear and tear on the thermistor component or moisture affecting the wiring harness.
Full guide for LED 1 fast pulseon 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