How to Descale a Water Heater

Descaling a water heater involves draining the tank, flushing it with a vinegar solution or commercial descaler, then refilling and testing the system to remove mineral buildup that reduces efficiency.

1. Kill the Power First. Switch off the circuit breaker for electric units or turn the gas valve to pilot for gas units. Close the cold water supply valve at the top of the tank. Wait 2-3 hours to let the water cool completely before proceeding.
2. Route Water Away. Attach a garden hose to the drain valve at the bottom of the tank. Run the other end to a floor drain, outside area, or large bucket. The hose end should be lower than the tank to ensure proper drainage.
3. Release System Pressure. Lift the lever on the temperature and pressure relief valve located on the side or top of the tank. This allows air into the system so water can drain properly. You'll hear air rushing in.
4. Empty It All Out. Open the drain valve by turning it counterclockwise. Water will start flowing out through the hose. This process can take 30-60 minutes depending on tank size. The first water out will be hottest, so keep clear of the hose end.
5. Blast Out Buildup. Once empty, turn the cold water supply back on briefly to create pressure that will flush out remaining sediment through the drain valve. Do this in 10-15 second bursts until the water runs relatively clear.
6. Mix Your Solution. Mix 4 gallons of white vinegar with 4 gallons of water for a standard 40-50 gallon tank. For stubborn buildup, use a commercial descaling solution following manufacturer instructions. The solution should fill about 20% of your tank capacity.
7. Pour In The Acid. Close the drain valve and disconnect the hose. Remove the cold water inlet pipe connection at the top of the tank. Pour or pump the descaling solution into the tank through this opening. Reconnect the cold water line.
8. Let Chemistry Work. Allow the descaling solution to sit in the tank for 6-8 hours or overnight. For heavy mineral buildup, you can leave it up to 24 hours. The acid will dissolve calcium and lime deposits during this time.
9. Flush Away The Gunk. Reconnect the garden hose to the drain valve and open it to drain all the descaling solution. Once empty, turn on the cold water supply and flush the tank thoroughly until no vinegar smell remains and water runs clear.
10. Power Back On. Close the drain valve and pressure relief valve. Turn on the cold water supply and let the tank fill completely. Once full, restore power to electric units or turn gas back on. Check all connections for leaks and test hot water at faucets within 30-45 minutes.