Every tank water heater slowly collects sediment: minerals from the water that settle on the bottom. A layer of it makes a gas heater rumble and pop, makes any heater work harder for the same hot water, and shortens the life of the tank. Draining it out once a year is the single most useful piece of maintenance you can do, and it needs only a garden hose.
Before you start: is it safe to flush yours?
If the heater is more than about eight years old and has never been flushed, think twice. Sediment can be the only thing plugging small holes in an old tank, and drain valves that have not moved in years sometimes will not close again. On a heater like that, flush gently, or leave it alone and start saving for its replacement.
What you need
- A garden hose
- A flat screwdriver, for some drain valves
- A floor drain, a sump pit, or a route to the outside for the hose. The water will be hot.
Step by step
- Turn off the heat source. For a gas heater, turn the control knob to Pilot or Vacation. For an electric heater, switch it off at the breaker. This matters: an electric element that heats with no water around it burns out in seconds.
- Close the cold water valve on the pipe going into the top of the tank.
- Let it cool if you can. An hour or two makes the job safer. If you cannot wait, take great care with the hose and the water.
- Attach the hose to the drain valve near the bottom of the tank, and run the other end to a drain or outdoors.
- Open a hot tap somewhere in the house. This lets air into the tank so that it can drain.
- Open the drain valve. Let the tank empty. The first water is often cloudy or sandy.
- Stir up what is left. With the drain still open, turn the cold water valve on for fifteen seconds and off again. Repeat until the water from the hose runs clear.
- Close the drain valve, remove the hose, and open the cold water valve fully. Leave the hot tap running until it flows smoothly without spitting air, then close it.
- Turn the heat back on. Only once the tank is full. Relight the pilot if your heater needs it, following the label on the tank.
Look at the drain valve an hour later. If it drips, a brass hose cap screwed onto it is a simple and lasting fix.
While you are there
- Temperature. 120°F is hot enough for a household and reduces the risk of scalding.
- The relief valve. This is the valve near the top with a small lever and a pipe running down the side. It is the heater's main safety device. If it drips constantly, or the pipe is missing, call a plumber.
- Look at the base. Rust stains or moisture around the bottom of the tank mean the end is near.
- The anode rod. A metal rod inside the tank corrodes so that the tank does not. Replacing it every few years can add years to the heater's life. It takes a large socket and some force, and many people leave it to a plumber.
How long should a water heater last?
Eight to twelve years is typical for a tank. The first four characters of the serial number on the label usually give the month and year it was made. If yours is past ten, plan the replacement now, on your own schedule. In New Jersey, replacing a water heater requires a permit and an inspection, which a licensed plumber arranges.
When to call a plumber
- Water leaking from the tank itself
- A smell of gas, or a pilot light that will not stay lit
- A relief valve that is dripping or discharging
- The drain valve is blocked solid, or will not close
- Rusty hot water, or very little hot water even after a flush
Find a licensed plumber near your town.