Boiler not working? How to diagnose a breakdown before you call an engineer

If your boiler is not working in October, work through this checklist before you call an engineer. Many breakdowns come down to something you can fix in under five minutes.

Check the basics first

• ◆Is the gas supply live? Check another gas appliance - cooker or gas fire. If nothing gas-powered works, call your gas supplier, not a heating engineer.
• ◆Is the boiler showing a fault code? Most modern boilers display a letter-and-number code on the panel. Look up your boiler model and code for a plain-English description.
• ◆Has the boiler lost pressure? The pressure gauge should read 1 to 1.5 bar when cold. Below 0.5 bar and most boilers will lock out. Top up via the filling loop as described in your manual.
• ◆Is the condensate pipe frozen? In cold weather the plastic pipe that exits through an external wall can freeze solid, causing a lockout. Pouring warm - not boiling - water over the pipe usually fixes it.

Restarting after a lockout

Many boilers lock out as a safety precaution and will restart after the fault is cleared. Look for a reset button - often marked with a flame icon - and hold it for three seconds. If the boiler fires and then locks out again, there is an underlying fault that needs an engineer.

Common fault codes explained

• ◆F.22 / E119 (Vaillant) - low water pressure. Top up via the filling loop.
• ◆F.28 / F.29 (Vaillant) - ignition failure. Usually a gas supply or ignition electrode fault.
• ◆E9 / EA (various brands) - overheat or safety shutdown. Check for blocked flue or airlock.
• ◆E1 (various brands) - ignition lockout. Reset and observe. Recurring means engineer needed.
• ◆F.75 (Vaillant) - pressure sensor fault. This usually needs an engineer.

When to call immediately

Call a Gas Safe engineer straight away if you smell gas near the boiler, see yellow or orange flames (they should always be blue), or the boiler is making loud banging or hissing noises. Do not attempt to reset or restart in any of these cases.

Frequently asked