Tankless water heaters provide endless hot water and exceptional energy efficiency, but they require regular maintenance to keep performing at their best. Cleaning a tankless water heater, also called descaling or flushing, removes mineral buildup that accumulates inside the heat exchanger and can reduce efficiency, increase energy costs, and shorten the unit’s lifespan.
Understanding why tankless water heater cleaning matters and how often to do it helps you protect your investment and maintain reliable hot water for years to come.
Why Tankless Water Heaters Need Cleaning
Unlike traditional tank water heaters that store heated water, tankless units heat water on demand as it flows through a heat exchanger. While this design eliminates standby heat loss and saves energy, it also makes tankless heaters vulnerable to mineral buildup.
Water contains dissolved minerals like calcium and magnesium. In areas with hard water, like Phoenix, these minerals are present in high concentrations. As water passes through the tankless unit’s heat exchanger at high temperatures, minerals precipitate out of the water and form scale deposits on the heating elements and inside narrow passages.
Over time, this scale buildup:
- Reduces heating efficiency by insulating the heat exchanger and forcing it to work harder
- Restricts water flow through the unit’s narrow passages
- Increases energy consumption as the unit struggles to heat water through scale-coated elements
- Triggers error codes when sensors detect abnormal conditions
- Shortens equipment lifespan by causing excessive wear on components
Regular cleaning prevents these problems and keeps your tankless water heater running efficiently.
How Often Should You Clean a Tankless Water Heater?
The frequency of tankless water heater cleaning depends primarily on your water hardness.
For hard water (above 7 GPG): Clean every 6-12 months
For moderately hard water (3.5-7 GPG): Clean annually
For soft water (below 3.5 GPG): Clean every 2-3 years or as recommended by the manufacturer
Phoenix has very hard water, typically measuring 12-18 grains per gallon. Most Phoenix homeowners should plan on cleaning their tankless water heater at least once per year.
If you have a water softener installed, you can extend the cleaning interval since softened water produces minimal scale buildup.
Signs Your Tankless Water Heater Needs Cleaning
Watch for these warning signs that mineral buildup is affecting your tankless unit:
Reduced hot water flow: Water pressure from hot taps is noticeably lower than cold taps
Inconsistent water temperature: Hot water fluctuates between hot and warm, or takes longer to reach the desired temperature
Error codes: The unit displays error messages related to flow, flame, or temperature sensors
Longer heating times: Water takes longer than usual to heat up
Strange noises: Popping, crackling, or rumbling sounds coming from the unit
Higher energy bills: Increased gas or electricity costs without a change in usage patterns
If you notice any of these symptoms, it’s time for a cleaning.
Tankless Water Heater Cleaning Solution
Professional tankless water heater descaling uses a mildly acidic solution to dissolve mineral deposits. The most common options include:
White vinegar: A natural, food-safe acid that works well for routine maintenance. Use 4 gallons for most residential units.
Commercial descaling solution: Specifically formulated for tankless water heaters, these solutions are more aggressive than vinegar and work faster. They’re ideal for units with heavy scale buildup.
Citric acid solution: Another natural option that’s slightly more effective than vinegar. Mix according to package directions.
Avoid using harsh chemical cleaners not designed for tankless water heaters, as they can damage internal components.
DIY Tankless Water Heater Flushing
If you’re comfortable with basic DIY tasks, you can flush your tankless water heater yourself. Here’s what you’ll need:
Equipment Needed
- Small submersible pump (1/6 HP)
- Two washing machine hoses (5-6 feet each)
- 5-gallon bucket
- 4 gallons of white vinegar or commercial descaling solution
- Adjustable wrench
- Towels for cleanup
Flushing Steps
1. Turn off the power and gas
For electric units, turn off the circuit breaker. For gas units, turn the gas valve to the off position.
2. Close the water valves
Close the cold water inlet valve and the hot water outlet valve on the tankless unit. These are typically ball valves located directly below the unit.
3. Open the service ports
Remove the caps from the cold water inlet and hot water outlet service ports. These ports have small valves specifically for flushing. Place towels underneath to catch any water that drains out.
4. Connect the hoses
Attach one hose to the cold water inlet service port. Connect the other end to the submersible pump.
Attach the second hose to the hot water outlet service port. Place the other end into the bucket.
5. Add cleaning solution
Place the submersible pump in the bucket and add 4 gallons of white vinegar or the recommended amount of commercial descaling solution.
6. Open the service valves
Open both service port valves (cold inlet and hot outlet) to allow solution to circulate through the unit.
7. Run the pump
Plug in the pump and let it circulate the cleaning solution through the unit for 45-60 minutes. You may see foam or sediment coming out initially, this is normal and indicates the solution is dissolving mineral deposits.
8. Flush with clean water
After the cleaning cycle, remove the pump from the bucket, empty the used solution, and refill the bucket with clean water. Run the pump for another 10 minutes to flush residual cleaning solution from the system.
9. Close service valves and remove hoses
Turn off the pump, close the service port valves, and carefully remove the hoses. Replace the service port caps, making sure they’re snug to prevent leaks.
10. Restore water and power
Open the cold water inlet valve slowly to refill the system. Check for leaks around the service ports. Once confirmed leak-free, open the hot water outlet valve and restore power or gas to the unit.
11. Test the system
Turn on a hot water tap and let it run for a few minutes to purge any air from the lines. Check that the unit fires up properly and delivers hot water at the expected temperature.
Professional Tankless Water Heater Cleaning
While DIY cleaning is possible, professional service offers several advantages:
Complete inspection: Technicians check all components, not just descaling the heat exchanger
Proper equipment: Professionals use powerful pumps and commercial-grade descaling solutions that work faster and more thoroughly
Filter cleaning: Service includes cleaning or replacing the inlet screen filter
Burner inspection: Gas units receive burner inspection and cleaning if needed
Safety checks: Complete system testing ensures proper operation and safety
Warranty protection: Some manufacturers require professional maintenance to keep warranties valid
For homeowners who aren’t comfortable with DIY maintenance or who have units with heavy scale buildup, professional cleaning is the better choice.
Preventing Mineral Buildup
Take these steps to minimize scale formation and extend time between cleanings:
Install a water softener: Treating hard water before it enters your tankless heater dramatically reduces mineral buildup. This is one of the most effective ways to protect your investment, especially in Phoenix.
Use a pre-filter: An inline sediment filter on the cold water line captures particles before they reach the unit.
Lower water temperature: Running your tankless unit at the lowest comfortable temperature reduces the rate of mineral precipitation. Most units don’t need to be set above 120°F.
Schedule regular maintenance: Annual professional service catches problems early and prevents heavy scale accumulation.
The Cost of Skipping Maintenance
Neglecting tankless water heater cleaning leads to expensive consequences:
Higher energy bills: A unit with scale buildup can use 25-30% more energy to heat water
Premature failure: Mineral deposits cause excessive wear on heat exchangers and other components, often requiring replacement years before the unit’s expected lifespan
Costly repairs: Ignoring minor issues leads to major component failures that cost hundreds or thousands to repair
Complete replacement: Severe scale damage can make repair impractical, forcing full unit replacement
Regular cleaning costs a fraction of what you’ll pay for repairs or early replacement.
Professional Tankless Water Heater Service in Phoenix
At Wyman Plumbing & Mechanical, we provide complete tankless water heater maintenance and cleaning for Phoenix homeowners. Our experienced technicians descale your unit, inspect all components, clean filters, and ensure everything is operating safely and efficiently.
We recommend annual maintenance for Phoenix’s hard water conditions. Regular service protects your investment, maintains energy efficiency, and ensures you always have reliable hot water when you need it.
Whether you have a gas or electric tankless water heater, we service all major brands and can handle any maintenance or repair needs.
Don’t wait for problems to develop. Call us at (623) 236-2097 or schedule tankless water heater maintenance online to keep your system running at peak performance.
