water heater bottom element not functioning after thermostat and element change
The manual you've provided doesn't show as much detail as I'd hoped, but it appears that your thermostat is identical to mine. To condense many weeks of fruitless service calls, I figured out my problem and it may help to resolve yours.

The temperature adjustment indicator may be out of kilter. The manual doesn't reference how to put it back into kilter, however. 

Consider for a moment that the water temperature at the thermostat is lower than you want it. You should be able to rotate the indicator and hear as well as feel the click as the thermostat engages. You may also hear a bit of sizzling as the element heats up.

What I discovered is that the technician who installed the second thermostat showed me how to calibrate it, by turning the indicator a number of times beyond the limit of the plastic needle, then turn it back to the desired temperature. It's a hit and miss sort of thing, but if you know the water temperature at the thermostat, you can get closer.

I used an IR contact-free thermometer to get in the ball park.

Unfortunately for me the second thermostat failed and the same tech who installed thermostats three, four, five and six forgot to perform the calibration. I'm not a water heater technician and also forgot the process until all parties involved were unhappy.

After hitting the tank area with the IR thermometer and trying to understand the disparity, I had an epiphany. Cranking away on the indicator put the thermostat on the mark.

Try the turn and click method to see that you are getting a response. If you turn and get no click, turn more!

If you have to drain the tank, there should be a port on the bottom to which you can attach a garden hose to minimize the mess.