Discovering water dripping from the bottom of your tankless water heater can be alarming. Even a small leak shouldn’t be ignored—left untreated, it can lead to costly water damage, mold, or even a complete unit failure. The good news is that most drips can be fixed with some basic troubleshooting and the right products. Here’s everything you need to know to diagnose, repair, and prevent a leaking tankless water heater—plus the best tools and parts to help you get the job done.
Quick Picks: Best Products for Fixing and Preventing Tankless Water Heater Leaks
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Best Overall Leak Fix Kit:
My PlumbingStuff Tankless Water Heater Flushing Kit – Removes scale that can cause seals and connections to leak. -
Best for Valve Replacement:
Rinnai Tankless Water Heater Isolation Valve Kit – Complete kit for replacing leaking service or flush valves. -
Best for Pipe Leaks:
SharkBite Brass Push-to-Connect Ball Valve – Quick, permanent solution for leaking supply lines or joints.
Why Is My Tankless Water Heater Dripping from the Bottom?
- Loose or leaking plumbing connections: Most leaks are due to loose fittings, failed pipe joints, or deteriorated seals at the cold or hot water inlet/outlet.
- Condensation: In humid climates or after heavy use, some water heaters “sweat”—but true leaks will not dry up after use.
- Leaking isolation or service valves: These are used for flushing and maintenance and can wear out or crack.
- Internal leaks from heat exchanger: If the leak is from inside the heater, it could signal corrosion, freeze damage, or a failed heat exchanger. This usually requires a pro or warranty replacement.
- Improper installation: Poorly sealed joints or mismatched fittings will drip sooner or later—especially after service or a flush.
- Drainage or pressure relief issues: Some units have a pressure relief valve that can drip if over-pressurized or faulty.
Step-by-Step: What to Do If Your Tankless Water Heater Is Leaking from the Bottom
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Turn Off the Power and Water Supply
For safety, switch off power at the breaker (electric) or close the gas valve (gas models). Turn off the cold water supply to the heater. -
Check for Visible Leaks
Use a flashlight to inspect all connections, pipes, and fittings at the bottom of the heater. Look for wet spots, mineral buildup, or rust. -
Dry and Monitor
Dry the area completely with a towel. Watch for new drips to locate the source. If the drip is slow, this may take a few minutes. -
Tighten Loose Fittings
If water appears at a threaded joint, use an adjustable wrench to snug it up (don’t overtighten). Add Teflon tape if you see leaks at threads. -
Check Isolation and Service Valves
Wipe dry and watch the hot/cold service valves and pressure relief valve. If any are dripping, consider replacing them with a new isolation valve kit. -
Inspect for Scale or Corrosion
If you see white mineral buildup or rust, flush the unit with a descaling kit to prevent further leaks. Corrosion inside the unit may require a professional repair. -
Examine the Heat Exchanger (if possible)
If water drips only during operation, and you can’t find any external leaks, the internal heat exchanger might be cracked. This typically needs expert diagnosis. -
Restore Power and Water, Then Test
Open water and power, then check for drips as the heater runs. Repeat inspections to ensure the leak is gone. -
Call a Professional If the Leak Persists
If you can’t find or fix the leak, or water drips from inside the sealed unit, contact a licensed plumber or the manufacturer for support.
Buyer’s Guide: Preventing & Repairing Tankless Water Heater Leaks
- Flush Annually: Regular descaling prevents mineral buildup that can crack seals and cause drips.
- Use Quality Fittings: Replace worn or cheap valves with high-quality isolation kits and push-to-connect valves for leak-free performance.
- Insulate Pipes: Protect exposed lines from freezing and bursting in cold climates.
- Check After Service: Always check all fittings after flushing or maintenance—most leaks start right after work is done.
- Watch for Error Codes: Some modern heaters alert you to leaks or low pressure—don’t ignore warnings.
- Warranty Support: Major leaks from inside the unit may be covered—check your model’s warranty before attempting major repairs.
Top Products for Stopping & Preventing Tankless Leaks
My PlumbingStuff Tankless Water Heater Flushing Kit
- All-in-one kit for removing mineral scale and buildup that can cause leaks
- Easy to use, fits all major brands (Rinnai, Rheem, Navien, Noritz, and more)
- Extend heater life and restore reliable operation
Final Verdict: The easiest, most effective way to prevent leaks from scale buildup.
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Rinnai Isolation Valve Kit
- Direct replacement for worn or leaking isolation/service valves
- Brass construction, easy install for DIYers
- Includes everything needed for a leak-free swap
Final Verdict: Best for fixing slow drips at the valve or after flushing.
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SharkBite Brass Push-to-Connect Ball Valve
- Instant, tool-free solution for leaky or hard-to-reach supply pipes
- Lead-free brass, corrosion-resistant
- Great for DIY or emergency repairs
Final Verdict: The easiest upgrade for leak-prone supply lines.
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Comparison Table: Leak Fixing & Prevention Products
| Name | Use | For | Key Features | Price Link |
|---|---|---|---|---|
| My PlumbingStuff Flush Kit | Descale, flush | All tankless units | Pump, hoses, bucket | View |
| Rinnai Isolation Valve Kit | Replace valves | Rinnai/all brands | Brass, easy install | View |
| SharkBite Ball Valve | Fix pipe leaks | 1/2″ or 3/4″ pipe | Push-to-connect | View |
FAQ: Tankless Water Heater Leaking from the Bottom
- Is a dripping tankless water heater dangerous?
Any leak should be fixed promptly to prevent electrical risk, mold, or serious water damage. Shut off power and water before repairs. - Can I fix a leak myself?
Most minor leaks at fittings or valves can be DIY repairs. Internal leaks or heat exchanger issues should be handled by a professional. - Why did my heater start leaking after a flush?
Fittings can loosen or valves may not seal properly after maintenance. Double-check and tighten all connections, and replace faulty valves if needed. - What if water is leaking from inside the unit?
This usually means a failed heat exchanger or serious internal issue. Contact your manufacturer or a licensed plumber for service or warranty support. - How can I prevent leaks in the future?
Flush your heater yearly, check fittings after any service, and replace aging valves or seals before they fail.
Conclusion
A dripping tankless water heater is more than an annoyance—it’s a warning sign you shouldn’t ignore. With the right tools and a little attention, most leaks can be fixed before they cause real damage. Take action now to protect your home, save money, and keep your tankless system running smoothly for years to come.