Why your tankless needs a flush every year (and what happens when you skip it)

A tankless water heater doesn't store water — it heats it on the way through a narrow copper or stainless heat exchanger. That's why it's efficient. It's also why it's vulnerable: every gallon of hard water that passes through leaves a little calcium and magnesium behind on those hot surfaces. In Utah County, where water routinely tests at 15–25 grains per gallon, "a little" adds up fast.

What scale does inside the unit

Scale is an insulator. As it coats the heat exchanger, the burner has to run hotter and longer to get the same water temperature. You feel it as:

• Slower hot water and temperature swings — the "cold sandwich" in the shower.
• Lower flow — the passages narrow, so less water gets through.
• Higher gas bills — the unit is working harder for the same result.
• Noise — popping or rumbling as water boils against scale.
• Error codes — most brands throw a maintenance or overheating code once scale gets bad enough.

Left long enough, scale cracks the heat exchanger. That's the most expensive part of the unit, and it's the part manufacturers won't cover if the failure was caused by mineral buildup.

The warranty part most people miss

Every major brand — Noritz, Navien, Rinnai, Rheem, Bosch — excludes damage from scale, lime, or "improper maintenance" in the warranty language. A 12- or 15-year heat exchanger warranty is only as good as your maintenance record. We keep that record for every customer, so if you ever need to make a claim, you have dated proof the unit was serviced.

What a flush actually does

We isolate the heater, connect a pump, and circulate a professional descaling solution through the heat exchanger for about 45 minutes. It dissolves the mineral layer without touching the metal. Then we rinse, check the inlet filter, and confirm flow and temperature are back to spec. The whole visit takes about an hour, and you'll usually notice the difference in the shower that night.

It's not the same as running vinegar through it. Vinegar is a weak acid; on Utah scale it mostly just gets the surface. A proper descaler clears the passages.

How often?

Once a year for most homes on the Wasatch Front. If you have a softener that's working, you can sometimes stretch it, but the manufacturers' guidance is still annual, and the inspection that comes with the visit catches other problems (a clogged inlet screen, a failing flow sensor, a venting issue) before they turn into a no-hot-water call.

What it costs

A Flush Pros visit is $225 flat: a $25 inspection plus the $200 flush. No trip fee, no upsell on the day. If you'd rather not think about it again, the Flush Club is $199/year, billed after the flush — we put your flush on the calendar every year, keep your warranty record, lock your price, and take 5% off add-ons and water treatment. What's included →