How to Flush Your On-Demand (Tankless) Water Heater with Vinegar

Tankless water heaters are efficient and long-lasting, but they do need routine maintenance to stay that way. Over time, mineral buildup—especially in homes with hard water—can slow performance, reduce hot water output, and force your system to work harder than it should.

A yearly vinegar flush is one of the simplest ways to keep your unit running efficiently. Here’s a straightforward guide you can follow at home.

What You’ll Need

• 4 gallons of white vinegar

• Submersible pump (tankless flush kit or utility pump)

• Two hoses

• 5-gallon bucket

• Screwdriver

• Towels (for drips)

Before You Begin

Make sure the unit is completely powered off:

• Turn off electrical power or flip the breaker

• Turn off gas supply (for gas models)

• Close the hot and cold water valves leading into the unit

• Let the heater cool before opening anything

Safety first.

Step-by-Step Instructions

1. Hook Up Your Hoses

Tankless heaters have built-in service valves for cleaning.

• Attach one hose to the cold service port (this pushes vinegar into the unit)

• Attach the second hose to the hot service port (this returns fluid to your bucket)

• Place both hose ends into an empty 5-gallon bucket

2. Add Vinegar & Prepare the Pump

• Pour 4 gallons of vinegar into the bucket

• Submerge your pump completely in the vinegar

• Make sure the return hose is positioned so it drains back into the bucket

3. Open Service Valves

Open both hot and cold service valves.
Keep the main water supply valves off during the flush.

4. Start Circulating

Turn on your pump and let the vinegar circulate through the heater for 45–60 minutes.

This dissolves scale buildup inside the heat exchanger.

5. Rinse the System

When the hour is up:

• Turn off the pump

• Close service valves

• Dispose of vinegar

• Refill bucket with clean water

• Circulate clean water for 5–10 minutes to flush out any remaining vinegar

6. Restore Normal Operation

• Close service valves

• Re-open main hot/cold water valves

• Turn power and/or gas back on

• Check for leaks

Your tankless heater should now run smoother, faster, and more efficiently.

How Often Should You Flush It?

Most homes: Once per year
Hard water homes: Every 6–9 months

If you’re seeing temperature fluctuations, noisy operation, or error codes, a flush is often the fix.

Want Someone Else to Handle It? Rim Rock Can Help.

If you’d rather not deal with pumps, hoses, and valves, Rim Rock Property Plus can do the entire flush for you—quickly and properly.

We provide:

• Tankless water heater flushing

• System inspection

• Maintenance package options

• Priority scheduling for Home Care Members

• Local, licensed, community-rooted service

📞 509-262-4630
🌐 rimrockpropertyplus.com

Start the year with a more efficient home — without the hassle.