Tankless Water Heater Maintenance: 4 Tasks for a Long Life

TL;DR: Tankless heaters last 20+ years — but only with a little yearly care, especially in hard water. Here's the routine.

_Last reviewed: July 2026 · 2 min read_

A tankless water heater can last 20 years or more — far longer than a tank model — but only if you keep mineral scale from clogging it, especially with hard water. Four tasks do it: descale yearly, clean the inlet filter, check the venting, and exercise the valves.

How do I descale a tankless water heater?

Flush (descale) the unit once a year to clear the mineral buildup that collects on the heat exchanger and chokes performance. Using the service valves, circulate white vinegar or a descaling solution through the unit with a small pump for about an hour, then flush with water. In hard-water areas, do it more often — scale is the number-one killer of tankless heaters. A water softener reduces how fast it builds.

Does a tankless heater have a filter?

Yes — clean the inlet water filter regularly. A small screen at the cold-water inlet catches sediment and debris; when it clogs, flow and heating drop. Shut off the water, remove the filter screen, rinse it clean, and reinstall. It's a quick task that keeps water flowing properly.

Why inspect the venting?

A gas tankless heater vents combustion gases, and a blocked or damaged vent is both a performance and a safety issue (combustion gases include carbon monoxide). Inspect the venting for blockages — debris, nests, or disconnected sections — and make sure it's clear and intact. Keep a CO detector nearby as a safeguard.

What does "exercising the service valves" mean?

The isolation/service valves let you flush the unit; if they're never moved, they can seize. Exercise the service valves periodically — open and close them — so they stay operable and ready for your annual descale. It's a 30-second task that saves a headache at flush time.

Track the annual flush

Tankless care is yearly, so it's easy to forget. Okoniq Property Hub keeps your descale date and notes with your home maintenance records in one private place.

Frequently asked questions

How often should a tankless water heater be flushed?

Once a year for most homes; every 6 months in hard-water areas. Letting scale build shortens the unit's life and can void the warranty.

Can I descale a tankless heater myself?

Yes — with a flushing kit (pump, hoses, bucket) and vinegar or descaler, it's a DIY job for most. If your unit lacks service valves or you're unsure, a plumber can do it and add valves.

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FAQ

How much does it cost to have a plumber descale a tankless water heater?

Professional descaling typically costs $150 to $300, depending on your location and whether service valves need to be installed. A DIY flush costs under $30 for vinegar or descaler and a basic pump kit if you don't already own one.

What happens if you never descale a tankless water heater?

Mineral scale builds up on the heat exchanger, reducing efficiency and water temperature until the unit eventually fails — often years earlier than its 20-year lifespan. Many manufacturers void the warranty if you can't show proof of annual maintenance.

Do electric tankless water heaters need descaling too?

Yes. Electric models develop the same mineral buildup on their heating elements as gas models, especially in hard water. The descaling process is identical: circulate vinegar or descaler through the unit using the service valves.

How do I know if my tankless water heater has hard water damage?

You'll notice inconsistent water temperature, reduced flow, or error codes related to overheating. If the unit struggles to reach set temperature or cycles on and off, scale has likely narrowed the heat exchanger passages.