Tankless Water Heater No Water Coming Out - Causes and Solutions
It can be incredibly frustrating when your tankless water heater stops producing hot water. You turn on the faucet expecting a steady stream of hot water for your shower or dishes, but instead you get nothing. What causes this lack of hot water flow in tankless heaters, and what can you do to get your hot water working again?
There are several potential causes for a tankless unit to stop producing hot water. The good news is that many issues can be resolved with some DIY troubleshooting and maintenance. However, more complex problems will require professional repairs.
Common Causes of No Water Flow
When your tankless water heater stops producing hot water, the issue is usually related to one of the following common causes:
Clogged Heat Exchanger or Water Filters
Hard water minerals and sediment accumulate inside the heat exchanger and filters over time. Excessive clogging restricts water flow, leading to limited or no hot water.
Frozen External Pipes
In cold climates, the external pipes feeding the heater sometimes freeze in winter. The water supply is blocked, preventing hot water output.
Closed Water Supply Valve
If the shut-off valve feeding water to your unit is accidentally turned off, you'll get no water flow. Open valves fully restore flow.
Tripped High Limit Switch
All tankless heaters have a high limit switch that trips if temperatures rise too high, indicating damaged internal parts. No water flows until this safety mechanism is reset.
Faulty Flow Sensor
Tankless heaters rely on flow sensors to detect incoming water. If the sensor is dirty, incorrectly calibrated, or defective, the unit won't fire up and heat water.
Bad Control Board
The control board is the "brains" directing all functions. If it's damaged or fails, it affects critical components like sensors, gas valves, circulating pumps, etc. No hot water results.
Pump or Recirculation Issues
Many tankless heaters use pumps and recirculation loops to deliver instant hot water. If these components fail, hot water won't make it to your taps.
DIY Troubleshooting Tips
Before calling for professional repairs, there are several basic troubleshooting steps you can take to get your tankless unit producing hot water again:
Check Water Supply and Valves
Verify water supply lines have no leaks, are turned on fully, and valves are open. Turn the unit's power back on once water flows correctly.
Inspect Filters and Heat Exchanger
Remove and clean filters of debris if they are visibly dirty. Descaling the heat exchanger can also remove stubborn mineral deposits.
Test Inlet and Outlet Temperature Sensors
Faulty sensors provide inaccurate data to the computer and disable heating. Replace damaged sensors.
Reset High Limit Switch
If temperatures rise too high, this safety switch trips. Locate it inside the unit and push reset button.
Confirm Flow Sensor is Working Properly
Use manufacturer instructions to test if flow sensor is correctly detecting water entering the unit, and replace if necessary.
Assess Control Panel and Circuit Board
Check for loose wiring connections, burnt circuitry, or corrosion on control panel and main circuit board. May require professional component replacement.
Investigate Pump and Recirculation Loop
If installed, ensure constant hot water recirculation pump is running and supply/return lines are not obstructed or leaking.
Professional Repair Options
For tankless water heater problems you can't resolve yourself, professional assistance is needed. Plumbers and HVAC technicians have specialized expertise, such as:
- Descaling and flushing the entire heat exchanger
- Replacing damaged water filters
- Installing heat tape on external pipes prone to freezing
- Testing and replacing non-functional sensors and flow detector
- Wiring and programming circuit boards
- Repairing recirculation pumps and loops
Professionals also have the proper equipment and tools for repairs residential owners lack. Be sure to get an accurate diagnosis of the issue before approving repairs.
Preventative Maintenance
While tankless water heaters are reliable, taking preventative steps maximizes operational efficiency and lifespan:
- Change filters and descale heat exchanger annually as routine maintenance
- Insulate outdoor water lines and pipes
- Confirm proper clearance requirements during initial install
- Plug unit into a surge protector Electrical spikes can damage controls
- Eventually upgrade to newer, more advanced technology
Tankless heaters with good preventative care can function effectively for over 20 years. But gradual mineral buildup or neglected maintenance almost always reduces performance over time.
When To Call A Professional
While no hot water flow often stems from minor fixable issues, you should contact a professional tankless water heater specialist if:
- Heat exchanger is extremely calcified or corroded
- Control panel and computerized board are non-responsive
- Circulation pump and supply lines require major repairs
- You've thoroughly tried standard troubleshooting with no results
Attempting complex repairs without proper tools, equipment, and knowledge may result in gas leaks, electric shocks, water damage or unit failure. The costs of professional assistance also help diagnose harder-to-identify underlying issues.
After 10-15 years, ongoing maintenance and minor repairs may no longer be worth the time, hassle and costs compared to a new unit installation. Replacing your tankless water heater makes sense if:
- Your model is over 15 years old. Newer technology offers better efficiency and reliability.
- Your heater is too small for increased household demand. Larger units have higher flow capacities.
- You experience multiple no hot water flow problems yearly, despite repairs attempted.
- Parts, including control boards and heat exchangers, become unavailable for older or discontinued models.
Review manufacturer warranties before purchasing a replacement. Also determine appropriate tankless heater sizing by household need to get the optimal unit.