A tankless water heater usually outlasts a tank heater by years, but how long yours lasts depends a lot on the water running through it and how it's been cared for.
The numbers
- Rinnai says its tankless water heaters have a life expectancy of up to 20 years, about twice as long as a tank heater.
- Rheem puts a typical tankless heater at 15 to 20 years or more with proper care, and says well-maintained systems can reach 25 to 30 years.
- Tank heaters, for comparison: the U.S. Department of Energy says most last 10 to 15 years, and Rheem puts the average at 8 to 12.
Those are the manufacturers' own estimates, for heaters that are installed right and maintained. Real life in the Valley can be shorter.
Why hard water matters here
East Valley water is hard: it carries a lot of dissolved calcium and magnesium. Inside a tankless heater, those minerals build up as scale on the heat exchanger. Scale makes the heater work harder and can restrict the flow. Rheem says yearly flushing or descaling clears that buildup, especially in hard water areas, and Rinnai says to flush the mineral deposits at least once a year. See flushing a tankless water heater for how it's done.
A tankless heater that's never been flushed in hard water is the one most likely to fall short of those numbers.
Signs yours is near the end
- The same error code keeps coming back, even after a flush and a service visit. See Rinnai error codes.
- Water leaking from the heater itself, not from a fitting that can be tightened or replaced.
- Hot water that swings hot and cold or runs out sooner than it used to, after scale has been ruled out.
- Repairs adding up on a heater that's already well into its second decade.
Not every error means replacement. Many problems turn out to be scale, a part or a setting. A plumber can tell you which it is before you decide.
How old is yours?
The manufacture date is usually on the rating label on the side of the heater, often coded into the serial number. If you can't read it, a technician can.
Getting the most years out of it
- Flush it on the schedule in your manual, at least yearly in hard water.
- Clean the inlet water filter screen when it's flushed. Rinnai says to check it periodically for debris.
- Consider a water softener. Softer water means less scale to begin with.
- Don't ignore error codes. A small problem caught early is cheaper than a heat exchanger.
OX Plumbing installs and services tankless water heaters across the East Valley: Rinnai, Rheem and Navien, gas and electric, and we pull the permits. We answer 24/7. Our $99 service call covers the visit, the diagnosis and an upfront price before any work.