Connecting the water
It is important to connect the HCW coil correctly. See below...
Note: MVM is used as a general term for an engine valve.
Mixing loop 1:
Principle: Variable flow in the primary circuit (supply) and constant flow in secondary circuit (VEX unit):

Mixing loop 2:
Principle: Constant flow in both the primary circuit (supply) and secondary circuit (VEX unit):

Do not connect the heating coil like this!
Connection without circulation pump risks of frost damage!

Explanation of simplified diagram:
