Low
S.28 on Vaillant ecoTEC exclusive System

Your boiler is temporarily pausing its heating cycle to prevent it from switching on and off too frequently after a short period of use.

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 anti-cycling time: Domestic hot water burner anti-cycling time

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 status occurs when your boiler has reached the required temperature too quickly and needs to pause for a few minutes before firing again. It usually happens because the heat has nowhere to go, often because your radiators are already warm or several thermostatic radiator valves have closed at once. By locking the burner temporarily, the boiler prevents unnecessary wear and tear caused by 'short cycling'.

This is more common in spring and autumn when the weather is milder and your home doesn't require the boiler to run at its full heat capacity for long periods.

DIY fix possible

Wait for 5 to 10 minutes for the boiler to complete its anti-cycling delay periodCheck that your room thermostat is set to the desired temperatureEnsure radiators are turned on to allow heat to dissipate

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