"The over flow is constantly running water"
That suggests that water is still going into the system from the filler pipe.
Are you SURE this has been shut off?
Continually filling the system which should have had a corrosion inhibitor added, means the inhibitor is becoming more and more diluted.
I would suggest you get hold of someone who is competent AND CERTIFIED to work on boilers, rather than risk any more guess and fiddling .