Three Shutoff Valves Are Being Used In This Shower System [See Warning At The Bottom Of This Page]

2009: Three shutoff valves are being used in this shower system

2019: The cold valve was eventually removed. Its backflow was messing up the tankless water heater's system.
It is better to leave the water heater at its default settings and then adjust the temperature at the remote control on the wall down to your preference.