gtxlr

Morning all, I'm looking for a bit of help with my downstairs WUFH system. It's a new build house with radiators upstairs and WUFH down stairs. It's running a myson manifold with 8 loops using a grunsfos upm3 pump. Heating is via a valiant 3.5kw (I think)heat pump. Control is via 4x myson thermostats downstairs and upstairs is a vaillant sensocomfort . In the utility cupboard is a Vaillant hot water cylinder and a vr71 and vaillant control panel. Now the issue I'm having is the downstairs WUFH manifold never goes above 20°c so when we turn the heating on via the myson manifold it's circulating cold water and this never heats up the flooring. The blending valve is set to 50°c and I can confirm the loops are flowing and have been bled. I'm guessing I need to raise this temperature but unsure how to proceed? I'm hoping it's just a settings issue.. Any advice is gratefully received, Chris