The new Bosch Therm 520HN that comes in either natural gas or liquid propane has 2 new control knobs for adjusting temperature and flow on the front of the heater as the older Bosch AquaStar 125 series heaters only had 1 control knob to adjust flow.
The Bosch 520HN has 2 control knobs on the front of the heater. The control knob on the left is the Power control knob and allows you to set the height of the burners for hotter temperatures or cooler temperatures. The control knob on the right is the Temperature Adjustment knob and is for adjusting the flow of water through the heater which has the ability to speed the flow of water up making it cooler or slowing it down and making it hotter.
Below is how turning the Temperature Adjustment knob effects the heater:
|Degree Rise||90° F||45° F|
|Activation Rate||0.5 GPM||1.1 GPM|
|Max Flow Rate||2.0 GPM||3 .7 GPM|
As the temperature adjustment knob is turned counter-clockwise, the output temperature will lower and the activation rate of the heater will be raised. Turning the knob clockwise will raise the temperature and lower the activation rate.
When turning the left Power Control knob to the left will give more power and higher water temperatures. Turning the knob clockwise will give less power and cooler water temperatures.
The Bosch Pro 520 HN has a gas control that modulates burner input in response to flow. Its purpose is to ensure that the hot water temperature will remain steady, although the water flow demand might vary.