Understanding the hot water system

Yes. The Powermax is a thermal store. This means it is full of hot radiator water, A coil of pipe is immersed inside carrying tap water. It enters the coil cold and comes out hot. The blender adds some cold if it is TOO hot.

When this pipe gets restricted badly with water scale, the water comes out hot but very slowly. The belnder has to hold back the cold pressure to prevent mixing occurring but eventually succumbs and lets cold water past. This results in higher flwo rate at cooler temperature. Your Powermax needs a descale and new blender valve.

Mike