BoilerFaultCodes.com
4 High Lockout

Your boiler has failed to ignite, which means it cannot heat up to provide warmth or hot water.

Call an engineer soon

Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description: N/A

What causes this fault?

This fault occurs when the boiler attempts to start up but cannot establish a stable flame after several tries. The most common reasons include a lack of gas supply to the unit, a dirty ignition probe that can't create a spark, or a block in the internal components that prevents the gas from flowing correctly.

This issue is more frequent during extreme cold snaps, as external gas regulators or pipes can sometimes freeze or experience pressure drops.

Typical repair cost £100-£350 (including labour)

DIY fix possible

Check if other gas appliances, like a cooker, are working to ensure gas is reaching your home.Inspect the condensate pipe outside for signs of freezing or blockage if the weather is cold.Press the reset button or turn the mode selector to 'OFF/RESET' for several seconds, then back to the heater icon.

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