Low
S.20 on Vaillant ecoTEC Plus 625

Your boiler is not broken; it is simply letting you know that it has received a request to provide hot water and is currently preparing to deliver it.

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

Hotwaterhandlingmode:Requirement

From this model's manual
Verified against the Vaillant Ecotec Plus 615 installation & service manual, page 38.
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 code appears when a hot water tap is opened or a shower is turned on, triggering the boiler's internal sensors to detect a flow of water. It signifies that the internal diverter valve has successfully shifted into position to prioritise heating your water. It is a normal part of the boiler's operation and simply confirms the system is responding to your request for heat.

DIY fix possible

No action is required as this is a normal status message and not a fault.Ensure your hot water taps are closed if you do not require water.Check your external controls or timer if the message stays on when no water is being used.

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