It is possible to convert some flipflop electric water heaters to operate the two elements simultaneously but as AOS points out you can't do that if the total amperage draw exceeds the circuit and equipment rating (say 40A). Watch out: setting any water heater to deliver temperatures above ...
the ignition control is tested in the same fashion as the safety devices. First, verify that it's receiving 20-28 volts. Then make a visual inspection of the unit and test for a spark at the pilot-burner electrode. Use caution around the electrode: It has low amperage but a high voltag...
After the installation of all water lines, open the main water supply valve and fill the heater. Open several hot water faucets to allow air to escape from the system while the heater if filling. When water passes through the faucets, close them and check for possible leaks in the system....