Low Information
S.3 on Vaillant ecoTEC exclusive

Your boiler is currently going through its starting sequence and is trying to ignite the flame to provide heating or hot water.

Monitor it

This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.

Technical description

Status indicator during start-up/heat demand sequence

What causes this fault?

This status occurs when the boiler begins its internal startup process to create a flame. It is a natural part of the ignition cycle where the fan, gas valve, and electrodes coordinate to light the burner. If this code stays on screen for a long time, it suggests the boiler is struggling to establish a stable flame to begin heating.

DIY fix possible

Wait for a few minutes as this is a normal status code, not a permanent fault.Check if your thermostat is calling for heat.Ensure your gas supply is turned on at the meter.

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