Low Information
S.21 on Vaillant ecoMAX System 612

Your boiler is currently preparing itself to provide hot water quickly and is not actually reporting a fault.

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

Pump and fan running (warm start)

What causes this fault?

This code appears when the boiler activates its pre-heat function to ensure hot water is delivered to your taps as quickly as possible. It is a standard operational sequence where the pump and fan run briefly to warm up the internal heat exchanger. Your boiler hasn't stopped working; it is simply preparing itself for use.

DIY fix possible

Check if the comfort mode or pre-heat setting is turned onWait a few minutes to see if the status changes to a normal heating codeMonitor for any actual fault codes starting with F if the boiler fails to fire

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