How do you know if your water heater is full?

The easiest, but messiest, way to check if your water tank is full is to head outside where the tank is and give a quick shot on the release valve. Water should squirt out at you. If your sole purpose is to make sure there is water there so you don't burn out your element, that's all you need to do.

Even if you're somehow in bypass mode with your tank full, your tank won't empty when you turn the taps on because water will come straight through the lines instead of from the tank. If, after a while, you're still not getting hot water, you know you're still in bypass mode, make the change and presto - hot water.

Thx everyone