What should I do when my boiler shows a fault code?

Boilers lock out to protect themselves, and a fault code identifies why. A few causes are within a homeowner's scope — low pressure, a frozen condensate pipe, a tripped supply. Everything else requires a registered engineer, without exception.

Safety

What you'll need

• The boiler manual
• Pressure gauge reading (optional)
• Warm water and a jug (optional)

Step by step

1. Look the code up in the manual or on the manufacturer's site.Codes are specific to the model. The manual usually distinguishes user-resolvable faults from ones needing an engineer, which saves an unnecessary call-out.
2. Check the system pressure.Low pressure is one of the most common lockout causes and it is a homeowner job. Between 1 and 1.5 bar cold on most systems.
3. Check for a frozen condensate pipe in cold weather.A common winter fault, often with a gurgling noise. The pipe is usually white plastic running outside. Warm water poured over it — never boiling — normally clears it.
4. Check the power and any external controls.A tripped breaker, a switched-off spur, a thermostat with flat batteries, or a timer that has reset after a power cut. All look like boiler faults and are not.
5. Check the gas supply is on.If you have a prepayment meter or other appliances also lack gas, the boiler is not the problem.
6. Reset once, following the manual.One reset attempt is reasonable. Repeated resetting of a boiler that keeps locking out is bypassing a safety mechanism.
7. Call a registered engineer for anything else.Ignition faults, fan faults, heat exchanger problems, repeated lockouts. Gas work is legally restricted and genuinely dangerous.
8. Note the code and the symptoms before calling.It saves diagnostic time and cost. Note when it happens, whether heating or hot water is affected, and any noises.

Tips

• Have the boiler serviced annually. Most faults develop gradually and a service catches them before a failure in the middle of winter.
• Photograph the boiler's model and serial number and keep it with your household records. Engineers ask for it every time.
• If a boiler is repeatedly failing and is old, ask the engineer directly whether repair or replacement is the better value. They will usually give an honest answer.

Common mistakes

• Repeatedly resetting a boiler that keeps locking out — The lockout is a safety mechanism responding to a genuine fault. Repeated resets bypass it rather than fixing anything.
• Attempting any work inside the boiler casing — Gas work is legally restricted to registered engineers in most countries, and the risks include carbon monoxide and explosion.
• Pouring boiling water on a frozen condensate pipe — It can crack the plastic. Warm water is what is recommended, applied gradually along the pipe.

Questions people ask