6699 Tankless Water Heater Flushing Kit Review: Does This $50 DIY Solution Really Work? (2025)

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When my Rinnai tankless water heater started displaying Error Code 11 (mineral buildup) and my hot water flow dropped to a trickle, the plumber quoted $350 for a professional flush. That’s when I discovered this tankless water heater flushing kit review research. After using the 6699 kit three times over six months, I’m ready to share whether this tankless water heater descaling kit actually saves money and restores performance – or if it’s just bucket with a pump.

The 6699 kit promises everything needed for DIY maintenance: 1/6HP submersible pump, 3-gallon bucket, hoses, and adapters for $40-60. But can this best tankless water heater flushing kit really match professional service at 1/6 the cost?

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Why the 6699 Kit Works

After three successful flushes restoring my water heater’s performance:

• Complete system: Pump, bucket, 2 hoses, 2 adapters, lid opener included
• 1/6HP pump: 1100 GPH flow rate, sufficient for effective descaling
• 3-gallon capacity: Holds enough vinegar solution for thorough cleaning
• Universal adapters: Fit most Rinnai, Rheem, Bosch, Navien models
• Reusable design: Pay once, use yearly (just buy $5 vinegar)
• 30-minute process: Quicker than waiting for plumber
• Cost savings: $350 professional flush vs $60 kit + $5 vinegar

Bottom line: This DIY tankless heater maintenance kit works. It saved me $300+ and restored full water pressure.

Related: Tankless Water Heater Maintenance Guide

Real-World Performance: My 6-Month Testing

First Flush: Solving Error Code 11

Problem: Rinnai RL75 displaying Error 11, reduced flow

Process (45 minutes total):

1. Closed water valves, connected hoses (10 min)
2. Mixed 2 gallons vinegar + 1 gallon water
3. Ran pump for 45 minutes
4. Flushed with clean water (5 min)
5. Disconnected, stored kit (5 min)

Results:

• Error code cleared immediately
• Hot water pressure restored to full
• Saved $350 plumber call

Vinegar solution color: Started clear, ended blue-green (mineral deposits)

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Effectiveness: Does It Match Professional Service?

According to multiple user reviews, the 6699 tankless water heater flushing kit performs identically to professional equipment. One plumber reviewer stated: “I use this exact setup professionally. Works just as well as my $300 commercial pump.”

Key effectiveness factors:

• 1100 GPH flow rate sufficient for thorough circulation
• 3-gallon capacity allows proper contact time
• Vinegar effectively dissolves calcium/magnesium deposits

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Step-by-Step: How to Use the 6699 Kit

Preparation (5 minutes)

1. Turn off power to water heater
2. Close isolation valves (hot and cold)
3. Remove service caps from valves
4. Gather supplies: Kit, 2 gallons white vinegar, bucket

Setup (10 minutes)

1. Mix solution: 2 gallons vinegar + 1 gallon water in bucket
2. Connect pump: Place pump in bucket, plug in
3. Attach hose 1: Pump outlet to cold water valve
4. Attach hose 2: Hot water valve to bucket (creates loop)

Flushing Process (45 minutes)

1. Open service valves slowly
2. Turn on pump
3. Circulate solution for 45 minutes
4. Monitor for leaks first 5 minutes
5. Check solution color (should darken = minerals)

Final Flush (10 minutes)

1. Drain vinegar solution
2. Add fresh water to bucket
3. Run pump 5-10 minutes (rinse cycle)
4. Close valves, disconnect hoses
5. Replace service caps
6. Restore power, test operation

Frequently Asked Questions for tankless water heater flushing kit review

Does this really work as well as professional service?
Yes. Professional plumbers often use identical equipment. The key is proper procedure – 45 minutes circulation time with vinegar solution effectively removes mineral deposits. I’ve used it three times with results matching my previous professional flush.

How often should I flush my tankless water heater?
Manufacturers recommend annually in areas with hard water (over 7 grains hardness), every 2 years in soft water areas. If you notice reduced flow or error codes, flush immediately regardless of schedule.

Can I use this on any tankless water heater brand?
The universal adapters fit most brands including Rinnai, Rheem, Bosch, Navien, Noritz, and Takagi. Check that your heater has isolation service valves with standard fittings. If not, you may need to install isolation valves first (one-time $50-100 cost).

Why use vinegar instead of chemical descaler?
White vinegar (acetic acid) effectively dissolves calcium/magnesium deposits, is environmentally safe, and costs $5 vs $20-30 for commercial descalers. Some manufacturers like Rinnai specifically recommend vinegar. For severe buildup, commercial descaler like Calci-Free or Flow-Aide may be needed.

How long does the flush process take?
Setup: 10 minutes, Circulation: 45 minutes, Final flush: 10 minutes, Cleanup: 5 minutes. Total: 70 minutes including prep. Faster than scheduling and waiting for a plumber (plus $300+ savings).

Is the pump loud enough to bother neighbors?
Yes, it’s noticeably loud – similar to vacuum cleaner volume. I recommend flushing during daytime hours and warning nearby neighbors if you live in apartment/condo. Wear hearing protection if noise-sensitive.

What do I do with the vinegar solution after flushing?
Pour it down a drain – vinegar is safe for plumbing and septic systems. The dissolved minerals wash harmlessly through drains. Some users save it for cleaning toilets or drains (still acidic enough to clean).

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Final Verdict

After three successful uses saving $900+ in professional service calls, the 6699 tankless water heater flushing kit is essential for tankless heater owners.

My rating: 4.5/5 stars

This tankless water heater descaling kit delivers professional results at DIY prices. Setup is straightforward, the pump is powerful enough for effective cleaning, and it pays for itself the first use.

Minor complaints (pump noise, basic hoses) don’t outweigh the massive cost savings and convenience of on-demand maintenance.

For anyone with a tankless water heater, this kit is a no-brainer investment that extends equipment life and maintains peak performance.