How to Flush a Water Heater
Flushing your water heater is one of the most straightforward maintenance tasks a homeowner can do, and in the Phoenix area, it's one of the most important. Mesa's hard water leaves behind mineral sediment every time water heats and cools inside your tank. Over time, that buildup reduces efficiency, makes noise, and shortens the life of the unit.
Here's how to do it yourself, why it matters more in Arizona than most places, and when it makes sense to call a professional instead.
Key Takeaways:
Mesa's 12-18 gpg hard water causes sediment to build up inside tank water heaters faster than the national average, annual flushing is essential.
For tank water heaters: turn off the heat source, connect a hose to the drain valve, shut off the cold supply, and drain until the water runs clear.
For tankless water heaters: circulate a descaling solution through the heat exchanger using a submersible pump, annually at minimum in the East Valley.
Call a professional if the drain valve won't reseat, sediment is extreme, or your unit is aging and overdue for a full assessment.
Regular flushing is one of the most effective ways to extend water heater lifespan in Arizona.
Why Flushing Matters More in Arizona
Phoenix metro water typically runs 12-18 grains per gallon, two to three times the national average. Every gallon of water that passes through your water heater leaves behind a small deposit of dissolved calcium and magnesium. In a low-hardness market, this accumulates slowly. In Mesa, it adds up fast.
The effects of neglected sediment:
Reduced efficiency: Sediment settles at the bottom of the tank, forcing the burner (gas) or heating element (electric) to work harder to heat the water above it. Your energy bill goes up; your hot water supply goes down.
Noise: That rumbling or popping sound from your water heater is sediment moving around as the water heats. It's not dangerous on its own, but it's a sign the buildup is significant.
Shortened lifespan: Sustained heat on a sediment-coated tank bottom accelerates wear on the lining. In Arizona, a neglected tank can lose years off its expected lifespan.
Inconsistent temperatures: Heavy sediment can interfere with the thermostat's ability to accurately read and maintain water temperature.
Annual flushing is the single most effective maintenance step for a tank water heater in a hard water area.
How to Flush a Gas or Electric Tank Water Heater
What you'll need:
Garden hose (long enough to reach a floor drain, driveway, or outdoor area)
Flathead screwdriver (some drain valves)
Work gloves
About 30-60 minutes
Step 1: Turn Off the Heating Source
Gas water heater: Turn the thermostat dial to the "Pilot" setting. This stops the burner from firing without extinguishing the pilot light.
Electric water heater: Turn off the breaker for the water heater at your electrical panel. Running the heating element without water in the tank can burn it out, this step is non-negotiable on electric units.
Step 2: Connect a Garden Hose to the Drain Valve
The drain valve is located near the bottom of the tank, typically on the front or side. It looks similar to an outdoor hose bib. Connect your garden hose and route it to a safe drain location, a floor drain, driveway, or outdoor area away from plants. The water will be hot and mineral-laden, and it will stain concrete if it sits.
Step 3: Let the Water Cool (Recommended)
Hot water coming out of a water heater can be 120°F or higher. If you have time, let the unit sit for an hour or two after turning off the heat source before draining. If you're working around a schedule, proceed carefully, keep the hose pointed away from people and plants, and wear gloves.
Step 4: Turn Off the Cold Water Supply
Locate the cold water shutoff valve at the top of the water heater (typically a lever or knob on the cold supply line) and turn it off. This stops fresh water from entering the tank while you drain.
Step 5: Open a Hot Water Faucet Somewhere in the House
Open a hot water tap, a bathroom sink or tub works well, and leave it open. This prevents a vacuum from forming in the lines, which would slow or stop the draining process.
Step 6: Open the Drain Valve and Flush
Open the drain valve on the tank. Water will begin flowing through the hose. Let it run until it flows clear, in a hard water area, the first water out may be discolored or carry visible sediment, which is exactly what you're removing.
Tip: If the water doesn't flow well or stops quickly, the drain valve may be partially clogged with sediment. Try briefly turning the cold water supply back on to stir up and flush the remaining sediment out. Repeat until the water runs clear.
Step 7: Close the Drain Valve and Refill the Tank
Once the water runs clear, close the drain valve securely. Turn the cold water supply back on and allow the tank to fill completely. Keep the hot water faucet you opened in Step 5 open, when a steady stream of water (not air) flows from that tap, the tank is full.
Step 8: Restore Heat and Check for Leaks
Gas: Turn the thermostat back to your desired temperature setting (typically 120°F). Electric: Turn the breaker back on at the panel.
Check the drain valve for drips or leaks. If the valve doesn't seat fully after being opened (common on older plastic drain valves), it may need to be replaced, a minor repair a plumber can handle quickly.
Allow 30-60 minutes for the water to return to full temperature before use.
How Often Should You Flush in Arizona?
Once a year is the standard recommendation for most homes. In Mesa and the broader East Valley, where water hardness is particularly high, some homeowners benefit from flushing every six months, especially if sediment is heavy during the annual flush or if the water heater is showing signs of reduced efficiency.
A quick rule: if the water during your flush runs discolored or carries visible particles, your current interval isn't frequent enough.
How to Flush a Tankless Water Heater
Tankless water heaters don't accumulate sediment in a tank the same way, but they have their own hard water vulnerability: mineral scale builds up on the heat exchanger, the component that heats the water on demand. In Arizona's hard water environment, this is the primary maintenance concern for tankless units and the most common cause of premature heat exchanger failure.
Flushing a tankless unit requires circulating a descaling solution (typically white vinegar or a commercial descaler) through the heat exchanger to dissolve mineral buildup. It's a different process from draining a tank.
What you'll need:
Submersible pump
Two lengths of hose
Five-gallon bucket
White vinegar (4 gallons) or commercial descaler
Isolation valves (most tankless units have these built in)
Step 1: Turn Off the Unit
Turn the unit to service mode or off, and shut off the gas supply (gas units). Do not shut off the electricity, most tankless units need power for the control board even during maintenance.
Step 2: Close the Hot and Cold Isolation Valves
Tankless water heaters typically have isolation valves on both the cold inlet and hot outlet lines. Close both valves to isolate the unit from the home's water supply.
Step 3: Connect the Flush Kit
Connect one hose from the submersible pump in the bucket to the cold inlet service port. Connect the second hose from the hot outlet service port back into the bucket. Open both service ports.
Step 4: Fill the Bucket and Run the Pump
Fill the bucket with approximately 4 gallons of undiluted white vinegar (or your descaling solution per manufacturer instructions). Run the submersible pump for 45-60 minutes, circulating the solution through the heat exchanger continuously. The vinegar dissolves mineral scale as it passes through.
Step 5: Flush with Clean Water
After the descaling cycle, drain the bucket, refill with clean water, and run the pump for another 5-10 minutes to flush any remaining solution from the unit.
Step 6: Reconnect and Restart
Close the service ports, reconnect the isolation valves to the open position, and restore gas supply. Restart the unit and check for proper operation.
How often: Annually for most Valley homes. If your unit doesn't have a water softener upstream, consider descaling every six months.
When to Call a Professional
DIY flushing is straightforward for most homeowners, but there are situations where calling a plumber is the smarter move:
The drain valve won't close fully after flushing. Old plastic drain valves often fail to reseat properly. A plumber can replace it quickly before a slow drip becomes a bigger problem.
Heavy sediment that won't clear. If flushing doesn't significantly improve performance or the sediment is extreme, a professional assessment can determine whether the unit is worth continuing to maintain.
Your tankless unit is unfamiliar territory. The flush kit setup and service port access on tankless units varies by brand and model. If you're not comfortable with the process, a professional descaling service is a reasonable annual expense, and it gives a technician a chance to check the full system while they're there.
Your unit is 8+ years old and you haven't flushed in years. On an older unit with heavy neglected buildup, a professional assessment alongside the flush can tell you whether continued maintenance or replacement is the better call.
Protect Your Investment
In Arizona, maintaining your water heater isn't optional, it's the difference between a unit that lasts 8 years and one that reaches 12. Annual flushing is the most accessible step any homeowner can take.
If you'd rather have a professional handle the flush, or if you want a full system check alongside the maintenance, Superstition Plumbing has been servicing water heaters throughout Mesa and the East Valley for over 45 years. Give us a call or schedule online.
