Low
S.34 on Vaillant ecoTEC exclusive System

Your boiler has noticed the temperature is very cold and has automatically turned itself on to prevent the internal pipes from freezing.

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

Heating mode: Frost protection (Frost protection mode active)

From this model's manual
Verified against the Vaillant Ecotec Exclusive Combi installation & service manual, page 42.
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 occurs when the boiler's internal sensors detect that the water temperature has dropped below 5°C. To prevent the unit from freezing and potentially bursting a pipe, the boiler automatically fires up the burner and runs the pump until the water reaches a safer temperature. This is a normal safety feature designed to protect your heating system during extreme cold spells.

This status code is almost exclusively seen during the winter months when external temperatures drop below freezing.

DIY fix possible

No action is required; this is a normal safety function.The boiler will stop this mode automatically once the internal water temperature rises sufficiently.Ensure your external condensate pipe is not frozen if the weather is extremely cold.

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