A professional plumber typically takes 60 to 90 minutes to complete a tankless water heater flush, including setup, descaling, and inspection. The actual circulation of the cleaning solution (usually white vinegar) generally takes 45 to 60 minutes.
Follow the instructions included in your manufacturer's manual to perform the flushing and draining procedure. This procedure may take up to 45 minutes.
Water heater service costs depend on your project and location. Check with a local pro for your specific job. Cost Insights: Tank water heater flushing costs $110 to $200, while tankless models run $150 to $250 due to their more complex components.
You might find that your tankless heater keeps turning off after you turn it on. This will, of course, prevent you from getting any hot water! There are a few possible causes for this, but the most common culprit is a clogged filter. Try replacing or cleaning your filter.
Here are some common reasons why your tankless water heater might not be working and how you can troubleshoot these problems.
A typical tankless water heater's lifespan often ranges from 15 to 20 years or more with proper care. In many cases, well-maintained systems can reach 25 to 30 years of service. That extended lifespan is one of the strongest considerations for homeowners researching how to choose a tankless water heater.
If the gas burner or electric heating elements come on during the flushing process, the water heater can be damaged, requiring repair or replacement. Some manufacturers will recommend turning the gas off completely during this process, others may recommend setting the gas valve to the “pilot” or “vacation” setting.
A 10-minute shower typically uses 20 to 25 gallons of hot water. Because showers are usually mixed with cold and hot water to reach a comfortable temperature, the actual volume of hot water drawn from your heater will usually be slightly less, while a low-flow showerhead can reduce this amount by up to 50%.
Water main flushing is the process of cleaning the interior of water mains and removing any accumulated sediment by sending a rapid flow of water through the mains. This rapid flow disrupts any sediment that may accumulate in the main over time, allowing us to filter and remove it.
Plumbers often hesitate to recommend tankless water heaters because they act like high-performance sports cars. Unlike traditional tank models that are "workhorses" and can function while mostly ignored, tankless units require precise installation, regular maintenance, and are highly sensitive to mineral buildup.
Gas tankless water heaters installed by December 25, 2025, might qualify for a $600 federal tax credit. The government is offered this 30% credit through December 2025 to help cover the cost of the unit and its installation. This tax credit comes from the 25C Energy Efficient Home Improvement Tax Credit program.
Yes, tankless water heaters need to be flushed regularly (typically once a year) to clear out mineral scale buildup, such as calcium and magnesium. Routine flushing maintains heating efficiency, lowers energy costs, and prevents clogs that can cause the unit to fail prematurely.
In short, draining removes water. Flushing removes sediment, and that makes all the difference.
Drawbacks of Tankless Water Heaters
As discussed above, the biggest downside of owning a tankless water heater is its higher cost. The initial installation and unit costs are more expensive than a traditional storage-tank water heater.
For larger households, multiple showers, laundry, and dishwashing may run at the same time. Hot water demand could reach 10–12+ GPM. A high-capacity tankless water heater—or even two units installed in parallel—may be the best solution.
The 4-minute shower rule is a sustainability and cost-saving initiative advising people to limit their daily showers to four minutes or less. This practice helps conserve water, reduce energy used for heating, and lower household utility bills by limiting consumption to approximately 36–40 liters (roughly 9.6–10.5 gallons) per shower.
Inside a house, toilets are the largest single consumer of water, making up about 24% of total indoor usage. Following toilets are showers and baths (20%), faucets (20%), and clothes washers (17%).
A 20-minute shower almost always uses more water than a bath.
If a standard showerhead is fitted, it will use around an extra half a gallon each minute, accounting for a 25-gallon emittance every 10 minutes, or 50 gallons throughout a 20-minute shower. *1 gallon = 4.54 litres.
You should never flush an older water heater (typically 5 to 10+ years old) that has never been flushed before. Accumulated sediment in old tanks can seal small rust holes or cracks; flushing this debris away can dislodge the seal and cause immediate leaks.
Flushing can be an important maintenance technique to remove stagnant water, restore disinfectant residual, remove loose deposits, and scour pipe surfaces. Flushing can reduce water age and address water quality complaints.
Here are six of the most common problems and maintenance concerns for tankless water heaters:
Tankless water heaters actually use less electricity overall than traditional storage tanks. The U.S. Department of Energy (DOE) estimates they are 24% to 34% more energy efficient for typical households, because they only heat water on-demand and eliminate standby heat loss.
A whole-home tankless water heater costs an average of $2,400, but costs can range anywhere from $1,600 to $3,800.