The answer to 'how to unclog water heater' is to drain the tank and remove any sediment buildup. First, turn off the power to the water heater and allow it to cool completely. Then, attach a garden hose to the drain valve at the bottom of the tank and run the other end to a floor drain or outside. Open the drain valve and let the tank fully empty. Once drained, close the valve and refill the tank. This will help remove any mineral deposits or debris that have accumulated and were causing the clogging.
If the clog persists or you're unsure how to properly drain the tank, it's best to call a professional plumber. They have the tools and expertise to safely and effectively unclog a water heater.