How Often Do Tankless Water Heaters Need Maintenance?

The manufacturer's interval is a starting point

Most manufacturers suggest descaling roughly once a year. That figure assumes water of average hardness, and it is written to cover a national market rather than any particular supply.

Treasure Valley groundwater carries a high mineral load. On untreated valley water, an annual interval is often not enough, and units that go two or three years between services frequently arrive with an exchanger that will not come clean.

What actually sets the interval

Water hardness. The harder the supply, the faster scale forms. This is the factor that matters most here.

How much hot water the house uses. A unit serving a family of five cycles far more than one serving a couple, and scale accumulates per litre passed, not per month elapsed.

Whether the supply is softened. A softener ahead of the heater slows deposition considerably, and it is the reason some houses genuinely can run to the manufacturer's interval.

Signs it is overdue

Hot water that fades mid-shower. Longer waits for temperature to arrive at the tap. The burner audibly cycling on and off during steady demand. Error codes relating to flow or overheating. Any of those on a unit that has not been serviced recently usually means scale.

The cheap version of this advice

If you do nothing else, have it descaled and have the inlet screen cleaned. If you want to lengthen the interval rather than just meet it, treat the water going in. Softening the supply is the only change that slows the process at the source rather than cleaning up after it.