What size is the Flow?
What size is the return?
How long are the dead legs to the last 3 rooms?
Is there a long dead leg to the last 3 rooms?
Is there a non return or check valve in the return line?
Does the return line connect to the cold supply?
Is the Circulation line properly insulated?
What is the draw off in the twenty units?
Who installed the Plumbing?
Have you called a professional Licensed Master Plumber?
Is the pump installed Properly.
Is the electricity to the pump connected properly?