How (and How Often) to Flush a Water Heater

Flush a tank water heater once a year. In areas with hard water, or if you have never done it, flush it every six months until the water runs clear, then settle into an annual rhythm. Flushing removes the sediment that collects at the bottom of the tank, which is the main thing that shortens a water heater's life and drives up its energy use.

Below is why it matters, a step-by-step for doing it yourself on a standard tank heater, and the cases where you should stop and call a plumber instead.

Why flush at all

Water carries minerals. As it heats, those minerals, mostly calcium and magnesium, drop out and settle at the bottom of the tank as sediment. Over time the layer thickens, and it causes real problems:

• Lost efficiency. In a gas heater, sediment insulates the water from the burner below, so the unit works harder and burns more fuel to heat the same water. You pay for it on the utility bill.
• Shorter lifespan. Sediment traps heat against the tank bottom, stressing the metal and the glass lining. A tank water heater is expected to last roughly 8 to 12 years; neglect pushes it toward the low end, and flushing pushes it toward the high end.
• Noise and reduced capacity. That popping or rumbling sound is water bubbling up through the sediment layer. The sediment also takes up volume, so you get less hot water.
• Premature failure. Enough sediment can clog the drain valve and accelerate corrosion, ending in a leak, which for a water heater means a flooded floor.

An annual flush is cheap insurance against replacing a several-hundred-to-over-a-thousand-dollar appliance early.

How to flush a tank water heater

This applies to standard gas and electric tank heaters. If you have a tankless unit, the process is different (it involves descaling with a pump and vinegar), and the manual is your guide. Read yours first.

What you need: a garden hose, a bucket, gloves, and a flat-head screwdriver. Allow about an hour, most of it waiting.

1. Turn off the heat. For a gas heater, set the thermostat to "pilot" or off. For an electric heater, switch off the breaker that powers it. Do not skip this; heating an empty tank damages the elements.

2. Shut off the cold water supply. Close the valve on the cold-water line into the top of the tank.

3. Let it cool, or plan for hot water. The water in the tank is scalding. Either wait for it to cool (safest) or work carefully, knowing the drained water will be hot.

4. Connect a hose to the drain valve. The drain valve is near the bottom of the tank. Attach a garden hose and run the other end to a floor drain, a driveway, or a large bucket. Downhill is easiest.

5. Open a hot-water tap. Turn on a hot faucet somewhere in the house. This lets air in so the tank drains smoothly, like lifting your thumb off a straw.

6. Open the drain valve. Let the tank empty. The first water out will likely be cloudy or full of grit. That is the sediment you are removing.

7. Flush with the cold supply. Once drained, briefly open the cold-water supply with the drain valve still open. This stirs up and pushes out remaining sediment. Repeat until the water running from the hose is clear.

8. Close up and refill. Close the drain valve, remove the hose, and reopen the cold-water supply. Leave that hot-water tap open until water runs steadily from it with no sputtering, which tells you the tank is full and the air is out.

9. Restore the heat. Only after the tank is completely full, turn the gas back to its setting or flip the breaker back on. Heating a partly empty tank ruins electric elements.

10. Record the date. Note that you flushed it, and when. This one habit turns "I think I did it last year" into a fact you can check.

When not to DIY

Stop and call a plumber if:

• The drain valve is stuck or leaks. Old plastic valves can crack or fail to reseal. Forcing one can turn a maintenance task into an emergency.
• You have never flushed a very old heater. Ironically, flushing a heater that is 10-plus years old and never serviced can dislodge sediment that was helping seal small leaks, and it may start weeping afterward. On a heater near the end of its life, weigh whether flushing is worth the risk or whether replacement is near anyway.
• You see rust-colored water or active corrosion. That can indicate the tank or anode is failing, and it is worth a professional look.
• It is a tankless unit and you are unsure. Tankless descaling is a different procedure; a wrong step can damage the unit.

There is no shame in hiring this out. A plumber will typically flush the tank and check the anode rod and valves in the same visit.

The anode rod: while you are at it

The anode rod is a sacrificial metal rod inside the tank that corrodes so the tank does not. It is the most overlooked part of water heater maintenance. Every few years, have it checked; a rod worn down to the core has stopped protecting the tank. Replacing a $30 anode rod is far cheaper than replacing the heater, but checking it means partly draining the tank, so many people fold it into a flush or leave it to a plumber.

Keep the record

Water heater flushing is an annual task that is easy to lose track of precisely because it comes around so rarely. Recording the flush date, the anode check, and any service protects the appliance and matters at resale and warranty time. A tank with a documented service history is worth more to a buyer and easier to make a warranty claim on. Keep it in your home maintenance log alongside the appliance details, and think about the water heater's age when you plan replacements; see how long appliances last.

Huswerks lets you set the annual flush as a recurring task with a reminder, and it stores the water heater's model, install date, and service history in one place. Free for one property. No card.

FAQ

How often should I flush my water heater? Once a year for most homes. Every six months if you have hard water or have never flushed the unit before. If the water runs clear quickly, you can settle into an annual schedule.

Can flushing a water heater cause problems? On a very old, never-flushed heater, yes, occasionally. Dislodged sediment can reveal leaks it was masking. If your heater is more than 10 years old and has never been serviced, weigh the risk or have a plumber do the first flush.

How do I know if my water heater has sediment buildup? Popping or rumbling noises during heating, reduced hot-water capacity, longer heat-up times, and higher energy bills are all signs. When you flush and the first water out is cloudy and gritty, that is the sediment.

Do tankless water heaters need flushing? Yes, but the process is descaling, not draining. It uses a pump to circulate vinegar or a descaling solution through the unit, usually once a year, more often in hard-water areas. Follow the manufacturer's instructions.

How long does a water heater last? A conventional tank heater lasts roughly 8 to 12 years; tankless units often last longer, 15 to 20 years, with maintenance. Annual flushing and periodic anode-rod checks push a tank toward the upper end of that range.

An annual flush is the kind of task that only works if something reminds you. Huswerks keeps the schedule and the service record. Free for one property. No card. → huswerks.com