Cold weather can turn your tankless water heater from a modern convenience into a frozen headache—especially if it’s installed in a garage, attic, basement, or outdoors. Frozen pipes and heat exchangers can shut down your hot water in an instant and, if not handled quickly, may even cause expensive damage. The good news? With the right approach, you can safely defrost a tankless water heater, prevent cracks, and get back to hot showers fast. Here’s your complete guide to defrosting, protecting, and maintaining your tankless system all winter long.
Quick Picks: Best Tools & Products for Defrosting and Protecting Tankless Water Heaters
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Best Pipe Heating Cable:
Frost King Electric Heat Cable Kit – Wraps around pipes and heater, automatically turns on below 38°F. -
Best Portable Heater:
Lasko Ceramic Portable Space Heater – Quick and safe heat for utility rooms, garages, or outdoor enclosures. -
Best Insulation Kit:
Frost King Foil Backed Pipe Insulation Kit – Prevents future freezing and saves energy.
Why Tankless Water Heaters Freeze
- Outdoor & Unheated Locations: Units in garages, attics, crawlspaces, or outside walls are most at risk.
- Power Outages: Many tankless heaters have built-in freeze protection—but it only works with electricity.
- Poor Insulation: Uninsulated pipes and units are vulnerable even in mild climates during cold snaps.
- Long Periods of Inactivity: If you leave home or don’t use hot water for days, standing water in the unit can freeze.
Step-by-Step: How to Defrost a Tankless Water Heater
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Turn Off Power and Gas
For safety, switch off the electrical breaker and close the gas valve before handling your unit. -
Check for Leaks or Cracks
Inspect your unit and surrounding pipes. If you see bulges, cracks, or water leaking as it thaws, call a plumber—do not turn the heater back on. -
Open Hot and Cold Taps
Open nearby hot and cold water faucets slightly. This relieves pressure and gives melting ice somewhere to go, reducing burst risk. -
Apply Gentle Heat to the Unit and Pipes
Use a hair dryer, portable space heater, or pipe heating cable. Move slowly along pipes and around the unit—never use open flames or heat guns. -
Monitor Progress
Keep an eye on the pipes and unit. Once water begins to flow, continue gentle heating until the system is fully thawed. -
Inspect Again Before Restarting
When fully thawed, double-check for leaks or cracks. Only turn power and gas back on when you’re sure everything is intact. -
Check Operation
Run hot water through the system and watch for normal function. Listen for odd noises or error codes, and inspect for leaks for the next few hours.
Important: Never force a tankless water heater to start if it is still frozen, leaking, or making strange sounds. If in doubt, call a licensed plumber.
Prevention: How to Keep Your Tankless Water Heater from Freezing
- Install Pipe Heating Cable: These plug-in cables keep pipes above freezing, even during power outages (if connected to a generator or UPS).
- Add Insulation: Wrap both the heater and exposed pipes with foam or fiberglass insulation for added protection.
- Use a Space Heater: In garages or outdoor enclosures, a small heater set to low can make a big difference during extreme cold snaps.
- Drip Hot Water Faucets: Letting hot water trickle during bitter cold keeps water moving and prevents freeze-ups.
- Check Built-In Freeze Protection: Many tankless models include built-in heaters or recirculation modes. Know how they work—and that they need electricity to function.
- Vacation Mode: Before leaving home for days, shut off and drain your tankless unit (see manual) or keep heating cables on.
Buyer’s Guide: Choosing the Best Freeze Protection for Tankless Heaters
- Automatic Heat Cable: Look for cables with built-in thermostats that only activate below 38–40°F.
- Length and Fit: Measure all exposed pipes and buy enough cable or insulation for full coverage.
- Safety Certifications: Choose UL-listed products for peace of mind.
- Energy Use: Pipe heating cables and small heaters use minimal energy—much less than fixing frozen pipes.
- Compatibility: Most products fit any brand—just match pipe diameter and voltage (usually standard 120V).
Top Products: Reviews for Defrosting and Freeze Prevention
Frost King Electric Heat Cable Kit
- Works on both metal and plastic pipes
- Thermostat turns heat on only when needed
- Simple installation, reusable every winter
Final Verdict: The single best way to protect exposed tankless water heater pipes.
See it on Amazon
Lasko Ceramic Portable Space Heater
- Compact, adjustable, and tip-over safe
- Quickly heats small utility rooms or closets
- Great emergency backup for deep freezes
Final Verdict: Perfect for supplemental freeze protection and fast defrosting.
Check price on Amazon
Frost King Foil Backed Pipe Insulation Kit
- Easy-to-cut, self-adhesive foam
- Keeps pipes and heater body warm longer
- Affordable and energy-saving
Final Verdict: The best value for long-term prevention and energy efficiency.
See details on Amazon
Comparison Table: Best Defrosting and Freeze Prevention Tools
| Product | Main Use | Automatic? | Portable? | Price Link |
|---|---|---|---|---|
| Frost King Heat Cable | Pipe/Heater Defrost | Yes | No | View |
| Lasko Space Heater | Room/Closet Heating | No | Yes | View |
| Frost King Pipe Insulation | Prevention/Insulation | No | No | View |
FAQ: Defrosting Tankless Water Heaters
- Can freezing crack a tankless water heater?
Yes—frozen water expands and can break internal heat exchangers, pipes, or valves. Always thaw gently and inspect for leaks before use. - How do I know if my tankless unit is frozen?
If you have no flow from hot taps (but cold water works), or see error codes, suspect freezing. Check for visible ice, condensation, or frosty pipes. - Should I use hot water or steam to thaw the unit?
No—use gentle, dry heat (hair dryer, heating cable, space heater). Avoid open flames or boiling water, which can damage parts and create hazards. - Will draining my tankless heater prevent freezing?
Yes—if you expect long outages or will be away, draining the system is the best way to avoid freeze damage. Follow your model’s manual for instructions. - Is freeze damage covered by warranty?
Usually not. Most manufacturers exclude damage from freezing—prevention is key!
Conclusion
A frozen tankless water heater is a hassle—but with careful thawing, proper prevention, and the right tools, you can avoid costly damage and restore hot water fast. Invest in quality pipe heating cables, insulation, or a portable heater before winter, and stay warm all season. Need more help or step-by-step advice for your model? Reach out anytime for expert guidance!