Common Boiler Error Codes Explained

Modern boilers show a fault code on their display when something's wrong. The exact codes vary by manufacturer and even by model generation, so treat this as a general starting point, not a definitive answer for your specific boiler - always check the code against your boiler's own manual or data plate too.

Worcester Bosch

• EA - often an ignition fault.
• D5 / CH low pressure - usually low system pressure, see our pressure guide.
• A1 / A6 - pump or sensor faults, generally need an engineer.

Vaillant

• F.28 / F.29 - ignition/flame faults.
• F.75 - water pressure or flow fault.
• F.22 - low water pressure specifically.

Baxi

• E133 - gas supply/ignition fault.
• E110 / E28 - overheat or fan fault.

What to do

Note the exact code, and whether it happened after something specific (a power cut, bleeding a radiator, cold weather). Low-pressure-related codes are sometimes fixable via the filling loop (see our pressure guide) - most others mean it's time to call a Gas Safe registered engineer rather than guess further. Never attempt to open the boiler casing or work on gas components yourself.