First, even if you burnt out your electric element, your gas would still heat the water. This points either to an open valve or incorrectly positioned valve on the bypass or a dead battery. The water heater is controlled by 12 volt. If the battery is low it will not work. Now, assuming your battery is good, start here.
Check your outside shower valves and make sure they are closed. Same with the inside shower.
Next hook up a water supply and fill the water heater tank with the pressure relief valve in the open position. When water starts coming out of it, snap it closed. Now you know you have water in the tank. Next turn on the electric to the water heater. You should be able to stand outside next to it and hear noises as it heats up. I'm sure you know it will take over an hour to get the water hot.
If you are not getting any noises outside and no warmth after half an hour or so your element may be burnt out.
Next try the gas. Again if you are outside you will be able to hear it fire up and burn. It either is or it isn't.
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