Low
S.46 on Vaillant ecoTEC plus Regular

Your boiler has detected very cold temperatures and has automatically turned itself on at a low setting 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

Frostprotectionmode(Comfort):Minimumload

From this model's manual
Verified against the Vaillant Ecotec Plus Regular installation & service manual, page 32.
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 to a level where there is a risk of freezing. To protect itself, the boiler automatically fires up at a minimum heat level to circulate warm water through the internal components. This is a normal safety function designed to prevent the heat exchanger from cracking due to ice expansion.

This status is almost exclusively seen during the winter months or during sudden overnight cold snaps when temperatures drop near freezing.

DIY fix possible

Check that your external condensate pipe is not frozenEnsure radiators are turned on and TRVs are open to allow water circulationWait for the boiler to finish the frost protection cycle; it will return to normal once the temperature rises

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