BoilerFaultCodesThe 3 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 49on 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