Low
S.0 on Vaillant ecoTEC System

Your boiler is working perfectly; it is simply in standby mode because your heating and hot water are currently at the temperatures you have set.

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.

What the manual says

Manufacturer manual

No heat required

From this model's manual
Verified against the Vaillant Ecotec installation & service manual, page 43.
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 status appears when your boiler's internal sensors detect that your home has reached the temperature set on your thermostat. Because the target temperature has been met, the boiler physically shuts off the burner to save energy and prevent overheating. It is essentially the boiler taking a nap until the temperature drops and it is needed again.

This code is frequently seen during the summer or shoulder months when your house stays warm enough that the central heating does not need to fire up.

DIY fix possible

Check if your room thermostat is set high enough to call for heatEnsure your programmer or timer is set to 'On' for heating or hot waterWait for the water temperature inside the boiler to drop, at which point the code will change as it starts firing again

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