[RussWhite]

Let me try to confuse you all.

There are two separate coolant ( anti-freeze ) circuits in our Aqua-Hots. One is engine coolant, the other the fluid in the AH boiler. They never mix if all is well.

The coolant in the boiler is circulated to different location in the coach depending upon the setting of thermostats.
The other circuit is contained in a heat exchanger inside the boiler. The engine coolant is circulated by the engine water pump when the engine is running, or by a a AH pump for engine preheat if it's cold and you turn it on.

So when you turn the valves off for say AH at the back of the coach you are stopping flow in engine loop only. You will not heat your boiler when driving and you will not be able to preheat the engine when desired.

If you turn the valves off for the heater, you are stopping flow to the heater core that is the heart of the dash air management system.
You may also have a AH radiator and fan up there or as in my case, the air from the AH radiator in the curb side bay may be ducted to outlets near the driver's and passengers feet. Got it? Russ