BoilerFaultCodesThe 6 most common faults
01
L- High DIY-safe
Your boiler has switched itself off for safety and is displaying a 'lockout' status, which will be accompanied by a second flashing code to tell you exactly what is wrong.
What to try first
Check the display for the secondary flashing number or letter that follows the 'L'Press and hold the 'Reset' button for two secondsCheck if your gas credit has run out or if other gas appliances are working
02
F- High DIY-safe
Your boiler has stopped working because it has detected a specific internal problem, which it will show by alternating the 'F' with another number or letter.
What to try first
Wait for the display to flash the number or letter following the 'F' to identify the specific fault.Try resetting the boiler by turning the mode knob to 'Reset' for two seconds and then back to the original setting.Check that your gas supply is active and your prepaid meter (if applicable) has credit.
03
L A High Engineer
Your boiler has detected that it is running much hotter than it should be and has switched itself off to prevent internal damage.
Full guide for L A04
H E High Engineer
Your boiler's internal computer is experiencing a communication fault and cannot control the system correctly.
Full guide for H E05
H9 High Engineer
Your boiler has detected that it is getting dangerously hot and has shut itself down to prevent damage.
Full guide for H906
L9 High Engineer
Your boiler has detected that it is becoming dangerously hot and has shut itself down to prevent any internal damage.
Full guide for L9on the Ideal Isar System
Ignition ElectrodePrinted Circuit Board (PCB)Gas ValveFanOverheat thermostatPrimary flow sensor
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