Hello,
With the mixing station you will find the return elbow will allow water to bypass the mixing valve to the return side of the manifold. You may need to close the supply valve at the top of the manifold and purge the loops backwords through the ruturn manifold and out through the supply purge point. Or flush the manfold with water in the top purge point and out the return purge point to get air out of the individual circuits. If you have other questions you can call into technical support anytime.