If your water heater has been making popping or rumbling sounds and you’re in a hard water area, don’t buy a new one yet.
Those sounds are almost always water boiling under a layer of calcium carbonate scale, not a failing tank. Scale forms when hard water heats up and minerals precipitate onto whatever surface is doing the heating. The scale insulates that surface, causes localized overheating, and produces the sounds you’re hearing.
A vinegar flush fixes this. It takes an afternoon and costs almost nothing.
What Scale Is Actually Doing to Your Heater
The Water Quality Research Foundation measured this. A 1/4-inch scale layer on an electric heating element reduces efficiency by approximately 40%. The element runs longer and hotter to compensate, and that’s what kills it early.
In a gas water heater, scale accumulates on the tank bottom where the burner heats from below. Same problem, same consequence.
A water heater in a hard water area, with no descaling maintenance, can fail 3-5 years earlier than one that’s been maintained. That’s a meaningful cost difference at $800-1,500 for replacement.
Tank Water Heater: Step-by-Step Descaling
Before you start: let the water cool completely. Scalding hot water in a tank under pressure is dangerous. Give it at least 2 hours after turning off the heating source.
1. Turn off the heater. For gas, turn the dial to “pilot.” For electric, switch off the breaker.
2. Wait for cooling. Two hours minimum. The water inside is very hot.
3. Connect a garden hose to the drain valve. The drain valve is at the base of the tank. Route the hose to a floor drain or outside. Open the valve and flush 5-10 gallons to clear sediment. Then close it.
4. Shut off the cold water supply. The supply valve is on the cold water line entering the top of the tank.
5. Open a hot water tap somewhere in the house. This relieves pressure and lets air into the system so water drains properly. Leave it open throughout the process.
6. Add the descaling solution. Two approaches work:
For a pump-circulated flush: connect a small submersible or transfer pump to circulate undiluted white vinegar through the drain valve connection and a hose going back to the cold inlet. Run this for 1-2 hours. This is the most effective method and uses less vinegar.
For a soak: if you don’t have a pump, drain the tank partially, introduce a 1:1 vinegar/water mixture (3-5 gallons total), refill with the mixture, and let it sit for 4-6 hours. The acid dissolves calcium carbonate on contact throughout the tank.
7. Drain completely. Open the drain valve and drain the vinegar solution fully.
8. Flush with fresh water. Close the drain valve, restore cold water supply, and let the tank fill. Then drain again. Repeat 2-3 times until the water runs clear and has no vinegar odor.
9. Refill and restore power. Once the tank is full (check by running the hot water tap you left open, water will flow steadily when full), close that tap, restore power or relight the pilot, and let it heat to operating temperature.
Tankless Water Heater Descaling
Tankless heaters have a sealed heat exchanger with dedicated service ports. The process is different from a tank heater.
Most manufacturers include a descaling port (two hose connections marked on the unit). You’ll need a small submersible pump, two lengths of washing machine hose, and a bucket.
Connect the hoses to the service ports. Put the pump in the bucket with 3-4 gallons of white vinegar or a 50:50 vinegar/water solution. Run the pump to circulate the solution through the heat exchanger for 45-60 minutes.
Most manufacturers sell a branded descaling kit with the correct hoses and pump for their units. That’s the easiest option, and it makes the process straightforward even if you haven’t done it before.
After circulating, flush with fresh water for 5-10 minutes before restoring normal operation.
Vinegar vs. Commercial Descaler
White vinegar (acetic acid) dissolves calcium carbonate slowly and safely. It’s the right choice for regular annual maintenance and light to moderate scale.
Citric acid solutions, CLR, and Lime-A-Way are more aggressive. They work faster on heavy buildup and are appropriate for heaters that haven’t been maintained in years or are in very high hardness areas (above 20 gpg). Rinse very thoroughly after using commercial descalers, multiple flushes.
How Often to Descale
At 7-10 gpg: annual sediment flush (no vinegar needed) plus a vinegar descale every 2-3 years.
At 10-20 gpg: annual vinegar flush.
At above 20 gpg (Phoenix, Las Vegas, San Antonio): every 6 months.
This is much less work than it sounds. Most of the process is waiting.
Preventing Scale Instead
A whole-house water softener prevents scale from forming at all. Softened water doesn’t precipitate calcium carbonate onto heating surfaces because the calcium and magnesium have already been removed. You’d still flush for sediment occasionally, but scale stops being a maintenance issue.
Salt-free conditioners (TAC systems) reduce how firmly scale adheres but don’t remove hardness minerals. They help, but they don’t eliminate the need for periodic descaling.
For the full picture on what a water softener does and doesn’t do, see how a water softener works. For a cost-benefit look at whether a softener makes financial sense for your situation, the hard water appliance damage page has the numbers. And water softeners vs. salt-free conditioners explains which approach makes sense when.