Hi, Hogrider
Welcome to the Forum.
Not knowing what kind of system you have, I can only guess
I guess the pump is running, but not sucking up the Antifreeze.
Did you close the valve coming from the water tank?
It could be pulling air from the tank..
Your pump may need priming, pour some antifreeze into the supply hose and raise it above the pump, or use air to blow it into the pump.
Hope this helps, and good luck