The temp gage goes up to about 80 and tends to stay right there, that's driving in 35-45 deg F. here. I'll give the disconnect a try. I re-checked the fluid, it's fine, I noticed one hose warm-hot while the other was cool so my assumption is that water is not flowing through. The heater radiator was checked for flow when they replaced the control head.

Is it possible that if someone had crossed the hosed from the heater core to the mono valve body that water would not flow because of the ball valve in the body?

Also, when you mention the CCU, is that a component other than the control head?