BoilerFaultCodesThe 6 most common faults
Your boiler is unable to start the small pilot flame needed to ignite the main heating system.
Why it happens: This fault occurs when the boiler's internal safety system detects that the small pilot light has failed to ignite or stay lit. Most commonly, this is caused by a blocked nozzle preventing gas flow or a worn-out sensor failing to tell the boiler that the flame is actually present.
Full guide for 47Your boiler is failing to keep the pilot light burning after you let go of the ignition button, meaning the heating cannot start.
Why it happens: This fault occurs when the boiler's safety monitoring system fails to detect a stable flame after the lighting process. The most common reason is a worn-out thermocouple that can no longer send a signal to the gas valve, or the overheat thermostat has tripped and cut the internal circuit to prevent damage. Essentially, the boiler shuts down the gas supply because it believes it is unsafe to stay running.
Full guide for 48Your boiler has successfully lit its pilot light, but the main burner is failing to ignite because it is not receiving the main supply of gas.
Why it happens: This fault occurs when the boiler successfully lights the small pilot flame but fails to transition to the main burner to heat your home. It is physically caused by a lack of gas flow to the main burner, often due to a faulty gas valve or a blockage in the pilot assembly that prevents the control board from seeing a strong enough signal to release the main gas supply.
Full guide for 49Your boiler's pilot light is failing to stay ignited after you try to light it, meaning the main burner cannot start to provide heat.
Why it happens: This fault occurs when the boiler's safety mechanism fails to detect a healthy flame, causing it to shut off the gas supply for safety. The most common reason is a worn-out thermocouple that can no longer generate the small electrical current needed to hold the internal gas valve open. It can also be triggered by a faulty overheat thermostat or a blockage in the pilot injector preventing a consistent flame.
Full guide for 51Your boiler has managed to start the small pilot flame, but the main burner fails to ignite to provide full heating.
Why it happens: This fault occurs when the boiler successfully lights the small internal pilot flame but the main burner fails to catch fire. The most common cause is a faulty gas valve that isn't opening properly to let the full flow of gas through, or a blockage in the main injector that delivers fuel to the burner.
Full guide for 52Your boiler is losing the water it needs to heat your home, which is likely caused by a slow leak somewhere in your radiators or pipework.
Check all radiator valves and visible pipework for signs of dampness or dripsLocate the external filling loop (usually a silver flexible hose) and carefully top up the pressure until the needle matches the red arrowMonitor the gauge and contact a professional if the needle continues to drop regularly
on the Ideal Mexico CF3 40 & 50
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