Anti-cycling time explained
To prevent the boiler from switching on and off constantly in a short time, this function adds a time delay. This function is used only for heating mode and not hot water. It is an electronic function, which means after the timer is activated, the boiler will wait until this timer is finished, and then resume firing as normal. The timer will again be activated each and every time the boiler needs to enter anti-cycling mode. This function is designed to prevent energy losses.
System Problems
While this is not a fault function in itself, the visibility of this function's symbol on the display for prolonged periods could indicate there are other issues at play, such as circulation problems or incorrect setup of the system. This would require an engineer to correctly determine the system issue. If you are an end user or home owner, it would be a good idea to record a video of what the screen is showing whilst the boiler is demanding heat. Patterns such as how fast the temperature rises or what other symbols are present can help identify issues.
Advanced Engineer Settings
If you are an engineer, the maximum anti-cycling time can be adjusted under the setting D.002 using the following table to produce the desired lockout time.
The adjustable range is 2 to 60 minutes, with the factory default set to 20 minutes. See Vaillant Diagnostic S & D Codes for more technical parameters.