Regularly flushing your Rinnai tankless water heater is one of the most important things you can do to keep it running efficiently, extend its lifespan, and prevent costly repairs. Hard water, even if you don’t notice it, leaves behind scale and mineral deposits inside your unit—reducing water flow, triggering error codes, and eventually causing damage. The good news? Flushing is easy with the right kit and a little know-how. This complete guide will walk you through the process, product picks, pro tips, and common questions.
Quick Picks: Best Flush Kits for Rinnai Tankless Water Heaters
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Best Overall:
My PlumbingStuff Tankless Water Heater Flushing Kit – All-in-one kit with pump, hoses, bucket, and descaler. Compatible with all Rinnai models. -
Best Budget:
Kelaro Tankless Water Heater Flushing Kit – Affordable and effective. Just add your own bucket. -
Best Premium:
Eccotemp EZ-Flush System Descaler Kit – High-powered commercial pump and professional results for tough scale.
How Often Should You Flush a Rinnai Tankless Water Heater?
- At least once a year for most homes
- Every 6 months if you have very hard water or notice reduced flow
- Before and after periods of heavy use, or after receiving error codes
Regular flushing keeps your Rinnai warranty valid and prevents those frustrating, expensive service calls.
What You Need to Flush Your Rinnai Tankless Water Heater
- Flush kit (pump, hoses, bucket, descaler or vinegar)
- Channel-lock pliers or adjustable wrench
- Gloves and old towels (in case of spills)
- Access to a nearby drain and electrical outlet
- User manual (for your specific Rinnai model)
Step-by-Step: How to Flush Your Rinnai Tankless Water Heater
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Turn Off Power and Gas
Switch off the electrical power to your unit. If it’s a gas model, close the gas shutoff valve. -
Turn Off Water Supply
Close both the cold water inlet and the hot water outlet valves going to and from the heater. -
Attach Hoses to Service Ports
Locate the hot and cold service valves (usually red and blue handles). Attach the flush kit hoses to these ports. -
Prepare Your Flush Solution
Fill the bucket with 2–3 gallons of food-grade white vinegar or descaler solution (follow flush kit directions). -
Connect the Pump and Bucket
Place the pump in the bucket and connect the hoses as follows:- Pump hose to cold water service port
- Return hose from hot water service port into the bucket
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Open Service Ports
Turn both service port valves to the open position (usually perpendicular to the pipe). -
Start the Pump and Flush
Plug in and turn on the pump. Circulate the solution through the heater for 45–60 minutes. The solution will dissolve scale and mineral deposits inside the heat exchanger. -
Shut Down and Drain
Turn off the pump. Close both service valves and carefully disconnect the hoses. Dispose of the used solution. -
Flush with Clean Water
Remove the bucket, fill it with clean water, and run the pump again for 5–10 minutes to rinse out any remaining vinegar or descaler. -
Restore the System
Remove hoses, close service ports, and open the main hot and cold water valves. Reopen the gas valve and restore power. -
Check for Leaks and Test
Run several hot water taps for a few minutes. Check all connections for leaks and listen for normal operation.
That’s it! Flushing your Rinnai heater once a year keeps water flowing strong and performance high.
Best Flush Kits for Rinnai Tankless Water Heaters: Reviews
My PlumbingStuff Tankless Water Heater Flushing Kit
- Powerful pump, durable hoses, 3.5-gallon bucket, and safe descaler
- Everything you need—no extra trips to the hardware store
- Reusable for annual maintenance
- Clear step-by-step instructions for all experience levels
Final Verdict: The best all-in-one kit for any Rinnai owner—easy, effective, and reliable.
See it on Amazon
Kelaro Tankless Water Heater Flushing Kit
- Budget-friendly, includes pump and hoses (bring your own bucket)
- Good for DIYers and small spaces
- Works with vinegar or commercial descaler
- Clear instructions and reliable performance
Final Verdict: Perfect for occasional use or if you already have a bucket.
Check price on Amazon
Eccotemp EZ-Flush System Descaler Kit
- Commercial-grade pump, extra-long hoses, pro-strength descaler
- Built for tough buildup or frequent use
- Ideal for multi-unit buildings or landlords
- Reusable and backed by a strong warranty
Final Verdict: A premium kit for anyone wanting fast, professional-quality results.
See details on Amazon
Comparison Table: Best Rinnai Flush Kits
| Kit Name | Includes | Pump Power | Bucket | Descaler | Price Link |
|---|---|---|---|---|---|
| My PlumbingStuff | Pump, hoses, bucket, descaler | 1/6 HP | Yes | Yes | View |
| Kelaro Kit | Pump, hoses | 1/10 HP | No | No | View |
| Eccotemp EZ-Flush | Commercial pump, hoses, descaler | High | Yes | Yes | View |
FAQ: Flushing Your Rinnai Tankless Water Heater
- What happens if I don’t flush my heater?
Scale buildup can cause poor performance, error codes, high energy bills, and eventual failure of the heat exchanger. - Can I use vinegar instead of a commercial descaler?
Yes—plain white vinegar is safe and effective for annual flushes. For heavy buildup, use a professional descaler. - Is flushing a DIY project?
Yes—if you have basic tools and a flush kit, most homeowners can do it in about an hour. Always follow your manual. - Will flushing fix error codes?
It often does! Codes related to flow, temperature, or scale are usually resolved by a thorough flush. - Do I need to flush if I have a water softener?
Yes, but you can do it less often—every 18–24 months instead of yearly.
Conclusion
Flushing your Rinnai tankless water heater isn’t just maintenance—it’s the key to efficient, endless hot water and avoiding costly repairs. With the right flush kit, you can do it yourself in an afternoon and keep your system running like new for years to come. Invest an hour now for comfort, peace of mind, and a lower energy bill all year.