High
F4 on Heatline Sargon

Your boiler has failed to start the flame needed to heat your home or water, often because internal waste pipes are clogged or the ignition system isn't sparking correctly.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Call an engineer soon

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

What the manual says

Manufacturer manual

Lockout due to ignition problem or Condensate Trap Blockage

From this model's manual
Verified against the Heatline Sargon 24 installation & service manual, page 26.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

Engineer required

This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Related fault codes

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