Boiler fault codes: what they mean and what to do

When a boiler stops, it usually shows a code on its screen. The code tells you, or your engineer, why it stopped. Many codes have a simple cause that you can fix yourself.

Find the codes for your boiler

Choose your make. Each page lists the common codes, taken from the maker's own website.

Codes can change between models, even from the same maker. Always check the user guide for your exact boiler.

Do these checks first

Whatever the code, these four checks fix a lot of breakdowns:

1. Check the pressure. Look at the gauge on the boiler. Most makers want 1 to 1.5 bar when it's cold. If it's lower, see how to top up low boiler pressure.
2. Check the gas. Does your hob work? If you have a prepayment meter, is there credit on it? Is the gas tap under the boiler open? On Ideal boilers, it's a yellow valve.
3. Check the condensate pipe. In freezing weather, the small plastic pipe outside can freeze. See how to thaw a frozen condensate pipe.
4. Check the power and controls. Is the boiler switched on at the wall? Do the thermostat and timer ask for heat?

Should I press reset?

Yes, once or twice is fine. A reset clears a one-off fault. If the cause has gone, the boiler starts again. Your user guide shows where the reset button is.

Don't keep pressing it. If the same code comes back, the boiler is telling you something is wrong. Some boilers even block you after too many resets. Ideal boilers show L5 when that happens.

Fault codes and lockouts

Some codes are warnings. The boiler may carry on, or try again by itself. Others are lockouts. The boiler shuts down and stays off until someone resets it. This keeps you safe when it can't light or gets too hot.

Makers show these in different ways. Ideal uses L for lockouts and F for faults. Baxi's newer boilers use H and E codes with full stops, such as H.02.07. Vaillant uses F for faults and S for normal status messages.

When to call an engineer

Call a Gas Safe registered engineer when:

• the code comes back after a reset;
• the code points to a part inside the boiler, such as the fan, a sensor or the gas valve;
• you see water leaking from the boiler, or smell burning;
• you're not sure what the code means.

Before you call, write down the make, the model and the exact code. It helps the engineer bring the right parts.

Not sure of your model? See how to find your boiler's model and GC number. It only takes a minute, and it means you'll read the right code list.