[Excaliber]

Perhaps there is a third port? I do seem to recall having to deal with some kind of plug at or behind the distributor? The water port directly behind the thermostat is used by the water temp sensor, which I don't really want to mess with. That port would normally be the supply of hot water to the heater box inlet. The water pump outlet is a no brainer of course and is the return of hot water port.

NOT the bypass hose, I don't think that would work out well at all for a heater application and could cause trouble in general for the pump or whatever.