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A little maintenance keeps a tankless water heater efficient for 20 years or more. Here is what to do, how often, and when to call a pro.
Good tankless hot water heater maintenance follows the schedule below, whether you do it yourself or book tankless water heater services from a pro.
| Task | How often | DIY or pro |
|---|---|---|
| Descale / flush heat exchanger | Every 12 months (6 months with hard water) | DIY or pro |
| Clean inlet water filter screen | Every 3–6 months and at every flush | DIY |
| Check for maintenance codes or scale alerts | Whenever displayed | DIY |
| Clean air intake filter (where fitted) | Every 6–12 months | DIY |
| Inspect vent and termination for blockages | Yearly, and after storms or snow | DIY visual, pro repair |
| Check condensate drain and neutralizer | Yearly; replace neutralizer media as instructed | DIY or pro |
| Test pressure relief valve | Yearly, per manual | DIY or pro |
| Combustion, gas pressure and burner inspection | Every 1–2 years | Pro |
| Check freeze protection on outdoor units | Before winter | DIY or pro |
Descaling, also called flushing, removes calcium and magnesium deposits from the heat exchanger. It is the single most important maintenance task. Our step-by-step guide explains how to flush a tankless water heater. You’ll need a flush kit and descaler and isolation valves on the unit.
Every tankless unit has a small mesh screen where cold water enters. Sediment can clog it, reducing flow and causing low pressure. Shut off the water, relieve pressure, unscrew the filter, rinse it, and reinstall.
Look for bird nests, leaves, snow or ice around the vent termination. Blocked vents cause error codes and safety shutdowns. Some units also have a washable air filter.
Condensing units drain acidic condensate. Make sure the drain line isn’t clogged or frozen and replace neutralizer media as the manufacturer recommends.
A licensed technician checks gas pressure, combustion, flame sensor, fan, venting seals and error history. Many brands offer extended warranties when you use their trained service network.
Navien tankless water heater maintenance and Rinnai tankless water heater maintenance both center on annual descaling and filter cleaning.
DIY works well for descaling and filter cleaning if your unit has isolation valves and you’re comfortable with basic plumbing. Hire a pro for gas, combustion or electrical checks, any repair, or if you see error codes you can’t clear. When searching for tankless water heater service near you, choose a licensed plumber with tankless experience and ask for an itemized price.
Professional tankless water heater maintenance services typically include a flush, filter cleaning and a combustion check. Servicing tankless water heater units yourself is fine for descaling but not for gas work.
| Option | Typical cost |
|---|---|
| DIY flush kit (pump and hoses) | $50–$150, reusable |
| Descaler per flush | $15–$40 (or white vinegar where allowed) |
| Professional flush | $150–$300 |
| Flush plus full inspection | $200–$350 |
| Adding isolation valves | $150–$400 including labor |
Costs are national estimates and vary by region.
Hard water is the main cause of tankless problems. A scale inhibitor or water softener reduces how often you need to descale.
Flush kits, descaler and isolation valves for every major brand.
Descale at least once a year, more often with hard water, and have a professional inspection every one to two years for gas units. Follow the schedule in your manual, since it can affect warranty coverage.
A professional flush and inspection usually costs about $150–$350 depending on your area. Doing it yourself with a flush kit costs about $50–$150 for the kit plus $15–$40 in descaler per flush.
Scale builds up in the heat exchanger, reducing efficiency and flow, causing temperature swings and error codes, and eventually damaging the heat exchanger. Scale damage may not be covered by the warranty.
Look for licensed plumbers who specialize in tankless units, ideally trained by your brand. Manufacturer websites often list service providers by ZIP code.
This guide is general information for U.S. homeowners, not professional advice. Gas, electrical and venting work must follow the manufacturer’s instructions and local codes, and in most areas requires a licensed plumber, electrician or gas fitter and a permit. Specifications and prices change; always confirm details on the product page and in the installation manual.
