I have hot water baseboard heating, zone valves on supply side or return side?

Hi I been having problem for past year now hot water comes from the cold side tap, I only have 1 tap that shares water hot and cold the other 2 I have are 2 separate hot cold and 2 are just cold taps now I have even shut the cold water supply to the hot water tank off, but yet when I run the...

Why we prefer installing the control valve in the return side rather than installing it in the supply side in A/C units

I read a previous answer about smells in bathroom lavatory, I have the same problem but its only on the cold side and thur out the house. I am a california plumber and have ran into this problem before, replacing the water heater and flushing the water lines did the trick. Now my question is my...