How important is the advice to drain your water heater once a year? Apparently it is really good advice to follow. I learned this just last weekend when I had to repair my nearly new water heater.
The problem was actually identified while some local technicians were servicing my gas furnace. Nearly the entire time they were working my gas water heater was on. Finally, the technician suggested that there may be a problem if it was regularly heating for such a long duration, especially when we hadn't just taken a shower or some other activity to use up an entire 50 gallons worth of water. Suddenly, I noticed that a fitting on my water softener began to leak and that the cold water feed line into the water heater was hot to the touch. The technician was worried I had the temperature setting too high, but this was not the case. The water heater was simply not shutting off properly. My water heater was not even three years old so I placed a call in to the manufacturer, Whirlpool, for help. They immediately sent me a new gas control valve. This part also includes the thermostat to determine when to begin heating and when to shut off.
The 
directions instructed me to shut off the gas, drain the tank, and disconnect everything. My first clue that something was wrong should have been apparent when the tank took more than two hours to drain. When draining a tank you not only need to shut off the cold water feed lines and open the drain, but also open a hot water faucet to release the water in the lines and the pressure on the tank. The reason for draining the tank is because the gas control valve, as mentioned before includes a sensor for the thermostat that inserts into the tank. When I pulled out my gas control valve water suddenly came gushing out as well. I hurried and stuck my thumb in the hole to stop the flow and cried for help. My wife brought down buckets and towels and we began draining the rest of the water in the tank. We were surprised to see that the water coming out was chunky and gooey. The water heater had failed to drain because the drain was clogged from the hard water deposits that had collected and settled in the tank. I was forced to unscrew the drain faucet in order to drain the tank fully.
I could see inside the tank that the bottom was still covered even after draining the tank of the water and white gelled mineral goo. I believe it was calcium? We opened the cold water line in short bursts to help flush out all of the chunks and rinse out the tank.
A few things we did to improvise along the way. The drain inlet was flush to the outside of the wall of the tank and would dribble water down the sides of the tank and made it difficult to catch the water in a bucket. The first improve was to cut the bottom out of a yoghurt container and slit it down the side so that I could roll it around the opening and provide a little clearance for the bucket to fit underneath. After an hour or more of draining and rinsing into a bucket I finally decided that another innovation was needed because I was getting tired of kneeling. Finally, we realized that our vacuum hose would fit around the opening and reach our drain. This was just what we needed to keep draining as we flushed out more chunks and goo.
To recap, the owner's manual care and maintenance includes a suggestion to fully drain the water heater yearly in order to flush out sediment and deposits that may have accumulated. A separate manufacturer's manual suggests to monthly drain off a few gallons instead of completely shutting off gas and all, for the same effect.
My suggestion: Drain your water heater yearly to help clean out the sediment and buildup that may occur. This will improve your water heater's efficiency and save you on your heating bill. It will also help to extend the life of your water heater
Hopefully, my experience will help some of you out there!
