Common Boiler Fault Codes: What They Mean and How to Repair Them

Is your boiler displaying an error code? This isn’t something you should ignore, even though it may only indicate a minor issue.

Modern boilers are pretty advanced, and are able to detect issues and shut down before a more serious issue arises. But this often leaves homeowners with a rather baffling error code to decipher, which can be especially difficult if you’ve lost your boiler’s manual.

Below, we’ll demystify boiler fault codes, explaining what each of the most common ones mean and how to repair them.

We’ll cover error codes from some of the UK’s biggest boiler brands, including Worcester Bosch, Baxi and Vaillant. Some you can tackle yourself, while for others you’ll need a Gas Safe engineer to repair your boiler.

Common Worcester Bosch Boiler Fault Codes Explained

• EA 227 – this can indicate a blocked or frozen condensate pipe, possibly due to debris or ice in cold weather. You may be able to thaw the pipe yourself, using hot (but not boiling) water.
• A1 – this means the water pressure in the system is too low, which could be due to a leak, or the bleeding or removal of a radiator. You can top up the pressure and see if it drops again. If it does, you might need to call in a professional to find the leak.
• C6 – the fan speed is too low, possibly caused by a blocked flue, control board issue or a problem with the fan motor. You’re likely to need a heating engineer for this one.
• E9 – this is a code associated with overheat lockout, which can be caused by an airlock in the system. Other possible culprits are faulty thermostats, or a faulty pump. You’ll need an expert to investigate.

Common Baxi Boiler Fault Codes Explained

• E125 – this could mean an overheat fault, which may be cleared if you bleed the radiators to make sure there’s no trapped air.
• E131 or E110 – this code refers to an overheat lockout, and may occur after a power cut. You can try resetting the boiler to see if it clears.
• E119 – this indicates low water pressure, so you’ll need to top it up and see if it drops again. If it does, it could be a sign of a leak – for which you’ll need a plumber or heating engineer.
• E133 – this is a gas supply fault, which can happen when prepayment meters are out of credit, or if the gas supply is turned off for any reason. If it’s neither of the above, call in an expert to investigate.

Common Vaillant Boiler Fault Codes Explained

• F22 – this is a fault related to low water pressure, where the system has shut itself off. You can try topping up the system (if you know how to do this safely). If the pressure falls again, it could be a sign of a leak.
• F23 – this is another safety shut-off related to water pressure, but this time because it’s too high. Check that filling loop valves are properly closed, and try bleeding a radiator to bring the pressure down to a safe level.
• F20 – this is a safety switch-off related to the boiler overheating. You need to leave it alone to cool down, before trying to turn it back on again. If the problem persists, call in a Gas Safe heating engineer to take a look.

Remember though that the codes above may only apply to specific models of boiler for each brand. If you have the manual for yours, use it to find out what the fault codes mean. If unsure, call in a boiler repair professional to check everything over.