You may have a build-up of limescale in the reflux head, due to extended use with hard water.
Another potential cause could be a build-up of algae or similar, depending on the water source you have used.
If you have run silicone oil through the reflux head (which is not recommended), the internal silicone seal may be damaged.
Please contact our Service team (firstname.lastname@example.org), and they will be happy to advise. Please include photos of your Carousel, and a description of your application and the problem you are experiencing.