What parts do I need to perform flow rate metering on the red Kombi3plus valve?

To meter the flow rate on the red valve of the Kombi3plus series you need
measuring adapter set VA3502A001 and a measuring device ( VM200A1001 or
VM241A1002). Measuring is always performed in the flow pipe, as regulation takes place in the return pipe.

Available from plumbing and heating system retailers and wholesalers.