The answer to 'how to unclog water heater installation' is to first drain the water heater tank to remove any sediment buildup that may be clogging the system. This is typically done by connecting a hose to the drain valve at the bottom of the tank and draining the water into a bucket or outside.
Once the tank is drained, you can try flushing the system by running water through the tank. You can do this by connecting a garden hose to the cold water inlet and letting it run for several minutes. This can help dislodge any remaining sediment or debris. If the clog persists, you may need to use a plumber's snake or auger to clear the blockage.