Water – Loosen the lower element on a electric water heater

I really question the wisdom of switching just the lower heating element. Doing so is going to overwork the upper element. I assume you are trying to conserve electricity, but this tactic is not going to be a great benefit to you. The upper element is used as the "quick recovery" unit that gives the cooling water from the lower part of the tank a boost as cold water is added as the hot water is used. If the water cools too much in the tank and you call for hot water, the upper element will not be able to keep up until the temp of the majority of the water warms up. I would suggest an inline switch or timer controlling both elements to help conserve energy and insulate the tank as much as you can. If you are looking for short, small quantities of hot water , you may consider a 1 or 2 gal point of use electric tank, in line at the specific appliance. There are several models to choose from at the box stores for under $300.00 I might add, if you do try this switch idea, you will need to switch both 120VAC lines with a DPST,(double pole, single throw) 30amp switch wired with 10AWG copper. When you open the thermostat cover, you will find the lines are connected to screw terminals on the thermostat switches.

If I understand correctly, your pilot flame is lighting correctly. But the main burner won't turn on because the electronics in the Gas Control Valve don't acknowledge the pilot is lit.

There are two likely faults:

1. Thermopile is not sensing the flame correctly, or
2. Circuit Board in the Gas Control Valve is defective.

To test for case 1, use a multimeter to measure the Thermopile output. It should be at least 350mV. Here are instructions on how to do that:

http://waterheatertimer.org/pdf/Test-thermocouple-and-thermopile.pdf

If the Thermopile output is less than 350mV, you may remove it from the burner and clean off any corrosion.

If the Thermopile output is adequate, the fault lies within the Gas Control Valve. Unfortunately, there are no user-serviceable parts in there, so you would need to replace that entire assembly.