My home was built in the 60's . I have a wood boiler hooked up to my oil . The problem I'm having is my dump zone doesn't work . When the home was built the zone valves were put on the return side . On the supply side there is a flo-control valve . The rads are cast iron with mono flo tee's . I am wondering why the flo-control valve was used ? Is it because the zone valves were on the return side or because the system has mono flo tee's ?