Tankless water heaters don’t service themselves. That’s the gist. The marketing on tankless units talks a lot about 18–22 year lifespans, but every one of those years assumes annual service — usually descaling, sometimes filter cleaning, occasionally a flame sensor wipe. Skip the service and you’re looking at 8–10 years before the heat exchanger gives up, which makes the upfront cost look a lot worse.
What Annual Service Actually Includes (in an Everett Home)
For most Snohomish County homes on City of Everett water (~50–70 ppm hardness, which we call “moderate”), annual service runs four things:
- Descaling the heat exchanger. Mineral buildup is the #1 cause of premature tankless failure. Even in our relatively soft water, scale accumulates in the heat exchanger over 12 months. We circulate a vinegar solution (or commercial descaler for heavier buildup) through the unit for 45–60 minutes, then flush with clean water.
- Cleaning the inlet filter. A small mesh screen at the cold water inlet collects sand, debris, and mineral fragments. Clogged inlet filter is the #2 cause of “my tankless is going cold” calls. Takes five minutes.
- Inspecting venting and combustion air. For gas units, we check the intake and exhaust vents for obstructions (bird nests, leaves, anything else that found a path in over the year). We also check combustion air supply is adequate.
- Checking gas line pressure. Tankless units are sensitive to gas pressure variation. We verify static and dynamic pressure with a manometer. Some older Everett homes have gas lines that drop pressure under demand, which makes the tankless underperform.
What You Can Do Yourself Between Visits
Two things, both quick. Clean the inlet filter every 3–6 months. There’s a small screen behind the cold water inlet — usually accessible by closing the shutoff valve, unscrewing the cap, and rinsing the screen. Owner’s manual will have the location. Five minutes of work that catches the most common performance issue we see.
Listen for unusual sounds during heat-up cycles. New popping, rumbling, or whistling sounds usually point to scale buildup well before performance drops noticeably. If you catch them early, descaling reverses them. If you don’t, the heat exchanger eventually fails. Our piece on why tankless units go cold mid-shower covers the most common warning signs, and our notes on setting the right temperature matter here too — running the unit hotter than necessary accelerates scale formation.
What to Avoid
Don’t descale with bleach. People have asked us. Bleach corrodes the heat exchanger materials and will void most warranties. Vinegar or a commercial descaler approved for your specific unit — those are the right tools. Don’t skip the flush step after descaling. Trace vinegar left in the unit can cause performance issues in the first day after service. And don’t try to descale a unit you don’t have isolation valves on — most modern tankless installs include service valves, but some older installs didn’t, and improvising with a hose and bucket is a recipe for floods.
If your tankless is over five years old and has never been serviced, that’s not unusual but it’s also why it’s struggling. We see that pattern weekly. Our complete water heater services include tankless service on annual schedules — we typically descale homes with us on a maintenance plan in September or October to make sure the unit can handle peak winter demand. Or reach the local water heater installation team directly to set up service.
