Low
S.25 on Vaillant ecoTEC Pro / ecoTEC Plus

Your boiler is temporarily cooling itself down after finishing a cycle for hot water.

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

DHW mode – pump or fan overrun error

From this model's manual
Verified against the Vaillant Ecotec Combi 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 occurs when the boiler detects that the internal heat exchanger is still too hot after you have finished using your hot water. To protect the components from heat damage, the boiler continues to run the pump or fan to dissipate the excess heat before it can start a new task. It is usually a normal safety function, but if it stays on the screen for a long time, it could mean a valve is sticking or the pump is starting to slow down.

DIY fix possible

Check that at least one radiator or bypass valve is open to allow heat to dissipateWait for the code to disappear naturally as the boiler settlesEnsure there is enough water pressure shown on the digital display (1.0 to 1.5 bar)

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