overdriv,
What kind of flow are you getting with that pump. Going by the meters on my manifold I barely get .1 GPM. LoopCad is saying my flow should be around .5 - .6
I have this manifold.
The flow meters are questionable, I do not go by them at all. I use a IR temp gun. You would be wise to do the same. If your pump is running and you have the valves on your loop open, all air purged, you are flowing water.
On low speed, the flow meters just barely show a flow, not even to .1 yet. On high speed with all 5 loops wide open, the flow meters show 1.0-something in between 1.5.
But, on high the water circulates through the loops so fast that there is hardly a temp drop across the floor.
If you would post a picture of your setup, you would get more help. I am far from a expert, I am still in my first full winter with this heat. I have mine set so it shows a 15-20 degrees temp drop across the floor.
Today it got up to 23*F over night and yesterday the wind blew and we got about 2" of snow, temps were in the low teens. My floor is 70* and the air in the shop is 64*. Thermostat is set for 64* air temp.
I post these facts so maybe you can get closer to where you need to be.