To unfreeze a tankless water heater, gently thaw the pipes with a space heater or heat tape, ensuring the unit is powered off and following safety precautions.
A frozen tankless water heater can leave you without hot water during the coldest months. Unlike traditional tank heaters, tankless models are more vulnerable to freezing because they don’t store hot water. This guide explains how to safely thaw your unit and prevent future freeze-ups.
Why Tankless Water Heaters Freeze
Tankless water heaters heat water on demand using powerful burners or electric elements. While energy-efficient, this design makes them prone to freezing because:
- No standing hot water to maintain warmth
- Small water passages ice up quickly
- Outdoor installations face direct cold exposure
According to plumbing experts, most damage occurs when frozen water expands inside the heat exchanger. This can crack critical components and void warranties.
Step-by-Step Thawing Process
Safety First
Before attempting to thaw your unit:
- Turn off power at the circuit breaker
- Close gas and water supply valves
- Open nearby hot water faucets to relieve pressure
Thawing Methods
For Indoor Units
- Use a hair dryer on low heat (keep 6 inches from components)
- Place a space heater 3 feet from unit (monitor continuously)
- Wrap pipes with heated towels soaked in warm water
For Outdoor Units
- Use a heat lamp or work light (avoid water contact)
- Apply electric heat tape to exposed pipes
- Build temporary insulated enclosure around unit
Never use open flames or excessive heat that could damage components. The Navien manufacturer recommends gradual thawing to prevent thermal shock.
After Thawing
- Check all connections for leaks
- Inspect the condensate drain line
- Restore power and test operation
- Monitor for error codes
If you notice leaks or the unit won’t power on, contact a professional immediately. For replacement parts, see our guide on tankless water heater components.
Preventing Future Freeze-Ups
For All Installations
| Solution | Effectiveness |
|---|---|
| Pipe insulation | Reduces freeze risk by 70% |
| Recirculation mode | Keeps water moving continuously |
| Generator backup | Maintains freeze protection during outages |
For Outdoor Units
- Install windbreaks or protective enclosures
- Use thermostatically controlled heat tape
- Consider relocating to garage or basement
Advanced Protection
Some premium models like the Rinnai RL94 feature dual freeze protection with:
- Electric heating elements
- Automatic water circulation
- Temperature-activated drain valves
When to Call a Professional
Seek expert help if you encounter:
- Visible cracks in the heat exchanger
- Water leaking from control panel
- Persistent error codes after thawing
- Gas smell near the unit
Proper maintenance and winterization can extend your tankless water heater’s lifespan and prevent costly freeze damage. Always consult your owner’s manual for model-specific instructions.
