how can i adjust the d.h.w blending valve on my powermax 155x combi boiler?

I need to reduce the tempriture of the domestic hot water to 43/45 0c at the draw of taps etc from the pre set temp of 58/60 0c, as set by the manufacturers.
If there is no adjustment available what alternative blender valve would fit inside the boiler casing and match the existing pipe layout?