How do you maintain a tankless water heater?
Updated August 2026
Tankless upkeep is basically one descaling flush a year (every 6 months on hard water), plus rinsing the cold-water inlet screen and air filter and paying attention to error codes. There is no tank to flush and no anode rod, but scale still builds inside the heat exchanger where you cannot see it. Stay on the schedule and the unit reaches its 15 to 20-year life; skip it and many manufacturers will void the warranty on a $3,000-plus appliance.
| Task | Interval | Effort |
|---|---|---|
| Rinse the cold-water inlet screen or filter | Quarterly | 10 min · DIY |
| Clear dust and lint from the air-intake filter | Quarterly | 5 min · DIY |
| Task | Interval | Effort |
|---|---|---|
| Flush the heat exchanger with vinegar or descaler | 12 months | 45–90 min · DIY |
| Wipe the exterior and check for leaks at the fittings | Yearly | 5 min · DIY |
| Log or clear any stored error codes | Yearly | 5 min · DIY |
| Task | Interval | Effort |
|---|---|---|
| Have a pro inspect venting and gas connections | 3–5 years | $100–200 pro |
What neglect costs
Skip the descaling and lime scale coats the heat exchanger, insulating it so the burner works harder for less hot water. You will feel it first as weaker flow and water that runs lukewarm, then as error codes and a heater that shuts itself down. Left long enough, scale ruins the exchanger, and a full replacement runs $3,000 to $4,500 installed. On hard water, most makers require documented annual descaling to honor the warranty at all.
Leave these to a pro
Descaling is a doable DIY job if the installer added isolation valves: a recirculation pump, two hoses, and a couple gallons of vinegar for $120 to $180 in gear you reuse every year. Without isolation valves, or if you would rather not, a plumber does the flush for roughly $150 to $300. Leave the gas and venting work to a pro entirely; a blocked exhaust on a gas unit is a carbon monoxide risk, not just an efficiency one.
This whole checklist ships as reminders in OnOtto: every task above, on the right schedule for your home, snooze-proof.
Load this checklist as remindersFrequently asked questions
How do you descale a tankless water heater?
Shut off the gas or power and the water, connect hoses to the two isolation valves, and circulate a few gallons of white vinegar or a commercial descaler through the heat exchanger with a small pump for 45 to 60 minutes. Then flush with clean water, clean the inlet screen, and restore service. A descaling kit costs about $120 to $180 and pays for itself the first year against a plumber's visit.
Do you really need to descale every year for the warranty?
Usually yes, especially on hard water. Many manufacturers make documented annual flushing a condition of the warranty, and they can deny a heat-exchanger claim if you cannot show it was done. Soft water buys you a bit more slack, but the exchanger still scales over time. Keeping the interval is what gets a tankless unit to its full 15 to 20 years rather than half that.
Why is my tankless heater going cold or throwing an error code?
Scale is the usual culprit: it restricts flow and trips the unit's safety limits, so it cuts out mid-shower and stores a fault. Other causes are a clogged inlet screen, a dirty air filter starving the burner, or an undersized unit hitting its flow limit. Start by cleaning the filters and running a descale; if the code returns immediately after, call for service.