High
F.29 on Vaillant ecoTEC plus Regular

Your boiler is trying to stay lit but failing, which means it has stopped producing heat and hot water as a safety precaution.

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

The burner fails to ignite after five attempts, the device does not start up and switches to “Fault”.

From this model's manual
Verified against the Vaillant Ecotec Plus Regular installation & service manual, page 33.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

What causes this fault?

This fault occurs when the boiler is running normally but the flame suddenly disappears and the system fails to relight it. The most common reasons include a temporary interruption in the gas supply, a blocked flue vent, or a buildup of carbon on the ignition electrodes that prevents them from detecting the flame.

This fault is more frequent during extreme cold spells, as frozen external condensate pipes can cause the boiler to back up and extinguish the flame.

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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