Low
S.10 on Vaillant ecoMAX 618

Your boiler is simply indicating that it is currently working to heat your hot water tank as requested.

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

Hot water demand (hot water operation)

From this model's manual
Verified against the Vaillant Ecomax 613 installation & service manual, page 45.
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 code appears when the external controls, such as a cylinder thermostat, signal the boiler to heat the water in your storage tank. It is not a fault, but rather a confirmation that the boiler has successfully switched its internal settings to prioritise your hot water supply. Once the water in the tank reaches the set temperature, this code will automatically disappear.

DIY fix possible

Check your cylinder thermostat or programmer to see if hot water is scheduled to be onWait for the boiler to finish heating the water tank, after which it should return to heating your radiatorsIf the code stays on for hours and you have no hot water, check that the tank thermostat is not set too high

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