Hi all   Been a while but have had my head well and truly in the build and work, nearly at moving in point...   We've finally turned on the ASHP and UFH today and am unable to get any sensible flow rate through the two Ivar mainfolds - some short loops (20m) can get up to 2l/min but that's all even with all  other zones closed off.  The manifolds are these: https://underfloorparts.co.uk/product/unimax-blending-10-port-underfloor-heating-manifold-with-grundfos-upm3-pump-u