I have an 8 loop stainless radiant manifold from pex supply. It has the valves and flow gauges. The only way I can get circulation is by backing the flow gauges out 3-4 turns. It worked fine untill a week ago. Is my pump taking a crap. I took one of the flow gauges out and examined it all looks fine. My pump is a 3 speed Grunfos 26-99 FC The pump is supposed to handle the head and flow on the low setting. I have been running it on high. The floor has 8-250' loops of 1/2" pex and less tha 10' of 1" copper to and from header. I have a b&g mixing valve. The loops flow unresrticted when I checked them. The flow gauges have not really worked good at all but they did flow for the first 2-3 weeks after install.