| Code | Brand | Generally means |
|---|---|---|
| EA | Worcester Bosch | Ignition fault — boiler failed to light |
| F28 / F29 | Worcester Bosch | Fault locked out after a failed ignition attempt |
| A1 / A6 | Worcester Bosch | Low system pressure |
| F.28 | Vaillant | Failed to ignite / loss of flame |
| F.75 | Vaillant | Poor circulation, low pressure or pump fault |
| F.22 | Vaillant | Water pressure too low |
| E133 | Baxi | No ignition, or gas supply interruption |
| E110 | Baxi | Overheat — the boiler has locked out for safety |
| E119 | Baxi | Low water pressure |
| F1 | Ideal | Low water pressure |
| F2 | Ideal | Overheat lockout |
| L2 | Ideal | Ignition failure |
| E133 | Potterton | Ignition or gas supply fault |
| E119 | Potterton | Low system pressure |
This is general guidance, not a diagnosis — the same code can point to more than one underlying cause depending on the model and history of the boiler. If a code keeps recurring after a reset, that's a sign it needs a proper look rather than repeated resetting.