The tank is already up against the rafters. What do you mean about increase cold feed. I have used 22mm. It seems to me that it is something to do with the nature of the flow at the junction of distribution and vent. I'm wondering if I changed the vent to run up vertically then horizontally...
Have just plumbed in a 160lt indirect tank in my loft with CWS on a platform above. Base of which is in line with top of tank. The horizontal pipe run to vent and distribution is about 750mm. The vent runs at an angle 45 degrees -ish to above the CWS.
On trying out the system I'm finding that...