I looked up the manual and got some answers.
The Aqua-Hot System is powered by TribridHot™ technology and uses one or a combination of the following sources:
1. The 120 Volt-AC Electric Element: When plugged into shore power, the electric element lets you use the power you are already paying for to provide heat and meet your light duty hot water needs.
2. The Diesel Burner: This is the Aqua-Hot’s most powerful heat source and provides all of heating and hot water needs in cold temperatures or dry camping.
3. The Vehicle’s Engine: When driving or idling, the engines surplus heat is transferred to the Aqua-Hot providing interior heat and limited hot water without burning any other fuel.
The Tempering Valve for the Aqua-Hot mixes the heated domestic water from the boiler tank with cold domestic water at the present ratio to reduce the risk of scalding. This valve is located in the back of the Aqua-Hot unit. Reference page 7 (part #19). To locate the Tempering Valve, remove the access cover page 7 (part #4) and then the thermostat access cover located above the burner. Reference page 7 (part # 19). The pink paint witness mark verifies that the Aqua-Hot is set at the correct factory setting and did not get tampered with during shipping or installation. Verify that the Tempering Valve is set at the proper temperature by using a digital thermometer at one of the hot water faucets. The water temperature should range between 115°F to 123°F. If the correct temperature cannot be set, please contact Aqua-Hot Heating Systems Technical Support Department at 1-800-685-4298 for additional assistance or visit our web site at www.aquahot.com