Not sure what you're asking really. The eberspacher heats an exchanger that your water runs through. Some are built with thermostatic valves to control the max temp.
Could be a lot of things. One, it's not hooked up, two, it's on a solenoid switch that needs to be turned on. If it's never worked and it's not your install, I'd lean towards #1. Follow the lines and look for a heat exchanger that your hot water line runs in to.