combination steam/hot water system

Mark_4

What is the best way to control the temperature of the water comming from a tube in shell heat exchanger. I was called to the job for circulator leakage & found the modulating valve controlling the steam had it's linkage (cam)missing& the valve stuck wide open.Then there is a three way valve which has been abandoned like a car in N.Y.C. all stripped apart. The system is only controlling commercial radiation to a few zones , no need for mixed water temps. Can I supply 180 -190* water from just the steam control valve or do I need the three way valve ? Suggestions? Mark