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Taco ZVC404 to Tekmar 508's
With the 500 series stats, you need to pull dedicated 24V power to C & R and then the Heat Terminals (5&6) go to the TT on the ZVC Control. (The ZVC control should have separate 24V power available to accomplish this).
If you are using a taco EBV, you would jumper terminals 3&4 on your zone valve terminals on the ZVC. It also may vary depending on where you choose to pull 24V from.