Currently have a 300 litre UVC ready for a heat pump to handle hot water + heating at a later stage but in the meantime like several others on the forum I would like to add a Willis heater between the manifold flow/return to run our UFH system.   System is 3 x 100m loops all to be run as one zone in a 100mm screed. Wunda manifold is installed minus a pump at this stage. Wiring wise 3 core + earth from the stat is in place and power can be added from the plant room board easily.