Boiler fault codes: what to do when your boiler shows an error

The short answer

A fault code is your boiler asking for help. Codes differ between makes and models, so the manual is the best guide to yours. Make the safe checks below. Then book a Gas Safe registered engineer if the code still shows.

Why codes differ

Every maker uses its own list of codes. The same number can mean different things on two boilers. Because of this, a web search for a code may point you to the wrong fault.

Keep the manual somewhere easy to find. If you have lost it, the maker’s website often offers a copy. Note the make, the model and the exact code before you ask anyone for help.

Safe checks you can make

These steps do not involve opening the boiler, so they are safe to try.

1. Check the display. Write down the code and any flashing lights.
2. Check the power. Make sure the boiler has electricity and the fuse has not tripped.
3. Check the controls. Look at the thermostat, the timer and the batteries.
4. Check the pressure. Low pressure causes many lockouts, and our boiler pressure guide explains the checks.
5. Check for leaks. Look for drips under the boiler and at radiator valves.
6. Check the manual. It will say whether a reset is safe and how to do it.

If the manual allows one reset, you can try it once. However, do not keep resetting, because a repeat code points to a real fault.

What never to do

Do not open the casing, because gas parts and live wiring sit inside. Do not try to repair any gas part. The Health and Safety Executive says gas work in a home needs a Gas Safe registered engineer. Its domestic gas FAQ explains how to check the ID card.

Our engineers are Gas Safe registered, so you can ask to see the card. Our boiler repair service takes requests through the form.

When it is an emergency

Some signs need action at once, because they put people at risk.

• You smell gas. Open windows, avoid switches and flames, and leave. Follow Cadent’s advice on gas smells.
• A carbon monoxide alarm sounds, or you feel dizzy or sick. Read carbon monoxide at home.
• Water is pouring from the boiler or pipes. Turn off the water at the stop tap, and see where your stop tap is likely to be.

A leak near the boiler may come from a burst pipe, so check the signs of a burst pipe too. If water is pouring out, follow the first 10 minutes of a plumbing emergency. For urgent plumbing help, our emergency plumber service takes requests at any hour.

When the fault is not the boiler

Sometimes the boiler is fine and the fault lies in the radiators. If some radiators stay cold while others heat up, read radiator cold spots. If you have heat but no hot water, see no hot water: what to check. A failing cylinder is covered in the hot water cylinder cost guide.

Repair or replace?

A code is not a reason to replace a boiler, since many faults are small. However, if the boiler is old and faults keep returning, replacement may give better value. ExpertSure says a single major repair can cost £300 to £500. Our new boiler cost guide sets out typical prices.

Landlords

A landlord must arrange an annual gas safety check, according to HSE. Tenants should report a boiler fault early, because delay can raise the risk. Our landlord plumbing checklist covers the duties in full.

What to tell the engineer

Good notes save time, so write down these points before you ask for help.

• The make and model of the boiler.
• The code, and when it first appeared.
• What the pressure gauge showed.
• Any noises, smells or leaks.

Photos of the display and the gauge help too. Our guide on how to choose a plumber lists what else to ask. You can type your notes into the form.

Frequently asked questions

Can I reset my boiler?

Your manual says whether a reset is safe. However, if the code returns, call an engineer.

Is a fault code dangerous?

Many codes stop the boiler as a safety step. Yet gas or carbon monoxide signs are always urgent.

Why does the code come back?

A repeat code points to a fault that a reset does not cure. Low pressure, a leak or a worn part are common causes, although only an engineer can tell.

Book an engineer

Use the online form and include the make, the model and the code. Mark it urgent if you have no heating in cold weather. Browse all our services or the areas we cover. Add your town and a short description, because that helps an engineer get back to you.

In Northampton, see boiler help in Northampton. Around Wellingborough, see plumbers in Wellingborough. Near Bicester, see plumbers in Bicester. In Buckingham, see plumbers in Buckingham. Coverage differs by area, so check the page for yours.