How a Professional Tankless Descale Actually Improves Performance

Most people know they “should” flush their tankless system once a year… but very few know what actually happens inside the unit that makes a descale so important. When I service a Rinnai unit here in Middle Tennessee, customers almost always say the same thing afterward:

“I didn’t realize it made this big of a difference.”

So here’s a simple explanation — written the way I explain it in someone’s home — of why a proper descale noticeably improves flow, temperature consistency, and overall performance.

What Scale Buildup Really Does Inside the System

• Reduces water flow internally
Scale acts like cholesterol in your plumbing. The heat exchanger gets coated, narrowing the water path.

• Forces the unit to work harder
When the burner has to heat water through scale, temperature swings become more common.

• Creates noise and vibration
Homeowners often think the unit is “going bad,” when it’s actually just fighting built-up minerals.

• Shortens the life of internal components
Sensors, screens, and temperature controllers all get stressed by mineral buildup.

What a Professional Descale Actually Does

• Restores proper water flow
After a flush, the difference in flow is one of the first things homeowners notice.

• Removes hidden buildup the eye can’t see
Even if the outside looks clean, the internal copper pathways can be coated with scale.

• Reduces temperature fluctuations
The burner can heat evenly again, making showers more consistent.

• Helps the system run quieter
A clean heat exchanger doesn’t struggle or vibrate like a dirty one.

Why DIY Kits Don’t Produce the Same Results

Here’s what I explain to customers who ask about DIY:

• Most DIY kits don’t circulate strong enough flow
Which means the descaling solution doesn’t fully reach every channel.

• Homeowners often skip the inlet filter cleaning
This alone can cut flow by 20–40%.

• They don’t test ignition patterns when finished
A proper service includes verifying temperature stability and burner function.

DIY is fine for very basic rinsing, but a full professional descale makes a measurable difference — especially on units 5+ years old.

The Bottom Line

If you’ve noticed lower water pressure, inconsistent temperatures, or noise coming from the tankless unit, those symptoms are almost always tied to scale.

A proper professional flush brings a Rinnai system back to how it should run. It’s one of the few maintenance tasks where homeowners can immediately feel the difference.