A tankless heater can last much longer than a tank heater, but only if it is looked after. The long figures you see quoted all come with a condition: regular maintenance. In a hard-water area, the biggest threat to a long life is scale. This guide covers how long the sources say tankless heaters last, what cuts that short, and how to decide between a repair and a replacement.
What the sources say
| Source | Tankless lifespan | Tank lifespan |
|---|---|---|
| U.S. Department of Energy | more than 20 years | 10–15 years |
| HomeGuide (2026) | 15 to 20 years, with some models lasting longer when maintained | Not given in the page we used |
| HomeAdvisor (2026) | around 20 years with proper maintenance | Shorter, per the same page |
The three sources land in the same neighborhood. DOE is the most generous. HomeGuide’s range is a little lower, and it says the top end depends on regular maintenance. DOE makes the same point in general terms: periodic maintenance can significantly extend your water heater's life and limit lost efficiency.
Why do tankless heaters tend to last longer? A tank holds hot water all the time, and the tank itself eventually corrodes and leaks. A tankless heater only holds water while it runs, and most of its parts can be replaced one at a time. The part that matters most, the heat exchanger, is also the part scale attacks.
What shortens a tankless heater’s life
Scale in the heat exchanger
The heat exchanger is the set of narrow tubes where the burner heats your water. Hard water leaves calcium scale on the inside of those tubes. Scale traps heat in the metal, narrows the tubes and makes the heater work harder.
The Battelle lab study for the Water Quality Association shows how fast that can happen on very hard water. Gas tankless heaters on unsoftened test water lost efficiency, falling from 80% to 72%, and had to be delimed after 1.6 years of equivalent service. Battelle also reported that every heater on unsoftened water was eventually pulled from testing because its outlet piping was clogged with scale buildup and flow could not be kept up. The test water was harder than most Utah city water, and the scaling was sped up, but the lesson holds: untreated scale ends a heater’s useful life early.
Ignored warnings
Most modern heaters warn you before scale gets serious. Rinnai’s code 14 means the heat exchanger has overheated, and the manual says to check for hot spots from scale. Navien’s E016 means the heat exchanger is overheating, with flushing among the remedies. Running a heater through repeated overheat shutdowns is hard on it. See tankless error codes for each brand.
Running it hot
Higher temperature settings speed up scale. Bosch notes that a softener is strongly recommended above 140 F outlet temperature. If you don’t need very hot water at the tap, a lower setpoint is easier on the heat exchanger.
Water above the brand’s limit
Each maker sets a hardness limit for its heaters. Many Utah cities publish figures above the Takagi and A.O. Smith limit, and some above the Navien, Noritz, Rinnai and Rheem limit. Our Utah hard water guide has the city data. Water above the line wears the heater faster, and several warranties exclude the damage it causes.
Repair or replace?
Start with what is wrong and what it costs to fix. HomeGuide lists these typical tankless repair costs:
| Repair | HomeGuide range |
|---|---|
| Minor repairs | $50–$300 |
| Pressure relief valve replacement | $80–$150 |
| Circuit board replacement | $400–$800 |
| Burner or heating element replacement | $400–$800 |
| Heat exchanger replacement | $600–$1,300 |
| More extensive repairs | $300–$1,300 |
Then compare that with the cost of a new heater:
| Replacement | Source | Range |
|---|---|---|
| Tankless heater installed, any fuel | HomeGuide | $1,400–$5,600 |
| Gas tankless installed | HomeGuide | $2,100 to $5,600 |
| Electric tankless installed | HomeGuide | $1,400 to $3,000 |
| Tankless heater installed | Angi | $1,406–$3,902, average $2,641 |
| Tank heater installed, for comparison | HomeGuide | $600–$3,100 |
No source gives a simple rule for when to replace. These questions usually decide it:
- How old is the heater? A heater well short of the lifespan ranges above is usually worth repairing. One near the end of them may not be.
- Is it still under warranty? A covered part changes the math. Remember that scale damage is usually excluded, so a scaled heat exchanger may be out of pocket even on a newer unit. See warranties and scale.
- What failed? A circuit board or burner on a heater with a sound heat exchanger is a repair. A failed heat exchanger out of warranty costs a real share of a new heater, so age matters more.
- Is the problem coming back? Overheat codes that return soon after a flush point to a deeper problem a technician should diagnose.
A technician can tell you which case you’re in. Book a repair diagnosis to find out.
What else goes into a replacement
A like-for-like tankless swap is the simpler job. HomeGuide puts installation labor at $600–$2,500 and permits at $50–$200. Converting from a tank costs more, because the gas line, venting or electrical service often has to change. Those items are covered on the installation page.
The only Utah-specific figures we found are dated. A HomeBlue estimate from January 2022 put a gas tankless installation in Salt Lake City at $2,500–$3,000. Prices have likely moved since, so use it only as a rough local reference.
Replacing a water heater is licensed plumbing work in Utah. Utah’s rule on minor plumbing work expressly does not include the installation or replacement of a water heater. See who can work on a water heater in Utah.
The ThermWise rebate
If you replace a gas heater, Utah’s gas utility may help. Enbridge Gas (formerly Dominion Energy) runs the ThermWise Appliance Rebates program. It offers $300 for a gas tankless water heater that is ENERGY STAR certified.
- The rebate request must be postmarked within six months of the installation date.
- For comparison, ThermWise offers $350 for a qualifying gas condensing storage heater.
- Questions go to the ThermWise Rebate Hotline at 1-877-932-0610.
Rebate amounts can change from year to year, so confirm the current figure before you buy. The federal tax credit that once covered gas water heaters applied only to improvements made through December 31, 2025.
Getting the most years out of yours
- Flush on your manufacturer’s schedule, sooner if your water is above its limit. See how often to flush.
- Consider a softener or scale-prevention system if your water is very hard.
- Don’t ignore reminder or overheating codes.
- Keep the setpoint no higher than you need.
- Keep dated service records.
When it’s time for a flush, book a tankless flush and descale.
Prefer to have it done? Call to book a flush.