How Long Do Tankless Water Heaters Last?

Article Summary

Tankless water heaters typically last 15 to 20 years with proper care—nearly double the lifespan of traditional tank water heaters. Water quality, maintenance habits, installation quality, and household demand all affect longevity. Hard water is the biggest threat, requiring annual descaling at $200+ per visit, but scale prevention technology eliminates this maintenance need and extends lifespan significantly.

This guide covers what affects water heater lifespan, warning signs of failure, and how to choose the right installer and system for your home.

Need a new tankless water heater, but not sure which model? Use the residential water heater selector tool to find options that suit your needs.

Average Life Expectancy of Tankless Units

Infographic comparing the lifespans of tankless and tank water heaters.

Tankless water heaters typically last 15 to 20 years with proper care and maintenance—nearly double the lifespan of traditional tank water heaters, which last 8 to 12 years.

Tankless units heat water on demand as it flows through the heat exchanger, eliminating the need for a storage tank. Without stored water, they avoid the sediment buildup and corrosion that shorten tank lifespans. On-demand heating also reduces wear and tear from constant reheating cycles.

Learning how tankless water heaters work makes the maintenance requirements easier. Your unit's actual lifespan depends on water quality, usage patterns, and maintenance habits. Professional installation and consistent maintenance help your unit reach or exceed that 20-year mark. Hard water is the biggest threat—mineral buildup damages heat exchangers over time if not addressed.

Not sure which tankless type you need? Learn the difference between condensing and non-condensing models.

Why Do Tankless Water Heaters Fail?

Infographic of how hard water damages tankless water heaters over time.

There are several reasons why water heaters fail, requiring repair or replacement. Early intervention and regular maintenance can often extend water heater lifespan.

Here's why tankless water heaters typically fail:

Hard Water Deposits: Minerals build up inside the heat exchanger, especially in hard water areas. Regular descaling resolves this, but severe buildup may require component replacement.
Heat Exchanger Leaks: Heat exchangers can start leaking after years of use. We recommend replacing the heater exchanger when this happens.
Excessive Water Pressure: High pressure stresses your system and shortens its lifespan. A pressure-reducing valve can help.
Undersized System: A unit that's too small for your household's demand works harder and wears out faster. Proper sizing during installation is critical.
Electrical or Ignition Problems: Faulty electrical connections in electric models or ignition system failures in gas models can cause intermittent hot water or complete shutdowns.
Ventilation Issues (Gas Models): Gas tankless water heaters need proper exhaust ventilation to safely expel combustion gases. Poor ventilation creates dangerous conditions and requires immediate professional attention.

Gas Leaks: Leaks from faulty valves, corroded connections, or worn gas lines pose serious safety hazards and need immediate repair.

Signs Your Water Heater Is Nearing the End of Its Lifespan

Electric water heaters, tank and tankless

Watch for these warning signs that your tankless water heater may need replacement:

Age: Check your unit's age using the serial number on the unit or in your manual. Tankless water heaters typically last 15 to 20 years.
Inconsistent Water Temperature: If your water goes from hot to cold without warning, or won't get hot enough, something inside has likely failed.
Reduced Flow or Pressure: When your hot water pressure drops noticeably, the heat exchanger might be clogged with minerals or failing.
Frequent Error Codes: When the same error code keeps popping up, you're probably better off replacing the unit than fixing it again.
Loud Noises: Banging, rumbling, or popping noises usually mean minerals have built up inside or parts are wearing out.
Water Leaks: Any leaking around your unit means seals are going bad or metal parts are corroding.
Rising Repair Costs: When repair expenses approach replacement cost, upgrading makes more financial sense.

Why You Should Replace Your Water Heater Before It's Too Late

Replacing your tankless water heater before it fails prevents costly water damage to your home and avoids the stress of emergency repairs. Planned replacements let you choose the right system for your needs rather than rushing during a crisis, and you can schedule installation at a convenient time instead of waiting days without hot water.

Newer models are also more energy-efficient with improved features like better temperature control and quieter operation, leading to lower utility bills and more consistent hot water delivery.

Ways You Can Extend Your Tankless Water Heater’s Lifespan

Annual Descaling: Hard water minerals require annual descaling at $200+ per visit. A.O. Smith's X3® Scale Prevention Technology eliminates this maintenance need.
Get Professional Installation: An undersized unit that can't keep up with your household's hot water demand works harder and wears out faster. Professional installation gets the sizing and setup right from the start.
Schedule Regular Inspections: Have a certified technician check your unit's heat exchanger, ignition system (gas models), and electrical connections annually to catch problems early.
Use a Water Softener: If you have hard water and a conventional tankless unit without X3® technology, install a whole-home water softener to reduce mineral buildup and corrosion.

Watch Your Water Pressure: High water pressure stresses your system. A pressure-reducing valve or thermal expansion tank protects against pressure-related damage.
Keep Vents Clear (Gas Models): Make sure exhaust vents stay clear and work properly. Blocked vents reduce performance and create safety hazards.
Opt for an Extended Warranty from the Manufacturer: Selecting the right water heater is the first step. An extended warranty provides peace of mind and can cover the cost of repairs or replacement parts.

Why Choose A. O. Smith for Tankless Water Heaters

For over 80 years, A. O. Smith has delivered reliable water heating solutions. Our ADAPT® tankless line includes X3® Scale Prevention Technology across all models, eliminating the annual descaling that costs $200+ per visit with conventional units. This integrated system can extend your water heater's operational life up to 300%, backed by a 15-year limited warranty covering scale-related failures.

Use our XPERT water heater selector tool to find the right ADAPT® model for your household, or connect with a certified installer near you for professional installation.

Frequently Asked Questions

Tankless water heaters typically last 15 to 20 years, while traditional tank water heaters last 8 to 12 years—nearly double the lifespan. Tankless units avoid the sediment buildup and corrosion that shorten tank lifespans because they don't store water. On-demand heating also reduces wear from constant reheating cycles.

Hard water mineral buildup is the leading cause of premature failure. Traditional tankless units require annual descaling at $200+ per visit to prevent heat exchanger damage. Other common causes include undersized systems, excessive water pressure, and poor installation. Extend your unit's lifespan by choosing proper sizing, maintaining consistent water pressure, and scheduling professional maintenance. Newer models with integrated scale prevention technology eliminate the descaling requirement entirely.