Tankless Water Heater Won’t Ignite? Causes, Fixes & Best Replacement Picks

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Are you frustrated because your tankless water heater just won’t fire up? You turn on the hot tap and nothing happens—the unit clicks, maybe flashes an error, but there’s no ignition and no hot water. This problem can strike anyone, and it always seems to happen at the worst time. Before you panic or call for an expensive service visit, take a deep breath. Most ignition failures are simple to troubleshoot, and some can be fixed with basic tools and a little know-how. Let’s explore the most common causes, what you can do right now, and the best replacement units if your system is on its last legs.

Quick Picks: Best Replacement Tankless Water Heaters

Why Won’t My Tankless Water Heater Ignite?

Tankless water heaters are sophisticated, but they all need three things to ignite: water flow, fuel (gas or electricity), and air. If any part of this system fails, you’re left with cold water and a cold shower. Here are the most likely culprits:

  • No Water Flow: If there isn’t enough demand, the unit won’t even try to ignite. Blocked filters or low pressure can be the cause.
  • No Gas or Power: Gas supply shut off, empty propane tank, tripped breaker, or unplugged unit all stop ignition.
  • Ignition Failure: The igniter itself can fail. Look for error codes or “clicking” sounds without flame.
  • Dirty or Clogged Components: Dirty flame rods, sensors, or blocked air intake will cause a shutdown.
  • Venting Problems: Improper or blocked venting keeps the system from starting for safety reasons.
  • Frozen Pipes or Water Lines: In winter, frozen lines can starve the heater of water.
  • Faulty Sensors or Circuit Board: Age and wear can cause control components to fail, especially on older units.
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Step-by-Step Troubleshooting: What to Do Right Now

  1. Check Power and Gas
    Make sure your heater is plugged in, the breaker is on, and the gas valve is open (for gas models). For propane, verify the tank isn’t empty.
  2. Inspect for Error Codes
    Most units display codes when there’s a problem. Consult your owner’s manual or look for a chart on the panel to see what the code means.
  3. Turn On Multiple Taps
    Tankless heaters need a minimum flow to activate. Open more than one hot tap to see if the unit responds.
  4. Clean Water Inlet Filter
    Sediment can clog the inlet filter, restricting flow and preventing ignition. Turn off water, remove, and rinse the filter.
  5. Check Venting and Air Intake
    Make sure nothing is blocking the vent or air intake—birds, debris, or snow are common problems.
  6. Inspect the Igniter
    If your unit is clicking but not lighting, the igniter or flame sensor might need cleaning or replacement.
  7. Reset the System
    Turn off the power for 60 seconds, then restart the unit. Sometimes this clears temporary glitches.
  8. Check for Leaks or Drips
    Leaks near the heater or on internal parts may trigger safety shutdowns.
  9. Descale If Needed
    Heavy scale inside the heat exchanger can block water flow and stop ignition. Regular descaling keeps your unit running smoothly.
  10. Review Installation & Settings
    New installs can sometimes have crossed pipes, wrong settings, or loose connections. Double-check everything.

When to Call a Professional

If you’ve tried all the above and your heater still won’t ignite, it’s time to call a licensed plumber or technician—especially for gas models. Issues like a failed gas valve, bad circuit board, or internal leaks are best handled by an expert. For units more than 10 years old, repair costs might approach the price of a new, more efficient heater.

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Product Reviews: Best Replacement Tankless Water Heaters

Rinnai V65iN Natural Gas Tankless Water Heater

Who it’s for: Families wanting dependable hot water and energy savings.
Key Benefits:

  • Compact, indoor-friendly design
  • Handles two to three hot water taps at once
  • Reliable electronic ignition and advanced safety features
  • Low operating costs with long-term warranty

Pros:

  • Consistent performance, year-round
  • Easy to maintain
  • Quiet operation

Cons:

  • Requires professional installation for gas
  • Initial cost higher than tank models

Final Verdict: One of the most popular and proven tankless models on the market.
Check price on Amazon

EcoSmart ECO 18 Electric Tankless Water Heater

Who it’s for: Apartment dwellers, small homes, or anyone wanting an electric alternative.
Key Benefits:

  • Compact, wall-mountable
  • Self-modulating technology for energy savings
  • Easy digital controls
  • Works with most standard electrical panels

Pros:

  • Affordable and efficient
  • Simple to install (with basic electrical experience)
  • Low maintenance

Cons:

  • Not as powerful as gas models for large homes
  • Requires 240V power

Final Verdict: A best-seller for small homes—delivers hot water quickly and reliably.
See on Amazon

Rheem RTGH-95DVLN High Efficiency Tankless Water Heater

Who it’s for: Large households or anyone who wants top performance and advanced features.
Key Benefits:

  • High efficiency for lower gas bills
  • Smart diagnostics and error monitoring
  • Handles simultaneous showers and appliances
  • Ultra-quiet operation

Pros:

  • Premium quality and reliability
  • Smart digital display
  • Excellent warranty

Cons:

  • Requires venting and pro install
  • Higher upfront price

Final Verdict: Ideal for busy families who want hot water on demand, all day long.
Check details on Amazon

Comparison Table

Name Key Features Specs/Capacity Price Link
Rinnai V65iN Gas, indoor, reliable ignition, compact Up to 6.5 GPM, natural gas, 10-year warranty View
EcoSmart ECO 18 Electric, digital, budget-friendly 2-4 GPM, 18kW, 240V, lifetime warranty (residential) View
Rheem RTGH-95DVLN Premium gas, high output, smart diagnostics Up to 9.5 GPM, natural gas, 12-year warranty View
See also  How to Service Tankless Water Heaters

FAQ: Tankless Water Heater Won’t Ignite

  • Why does my heater click but not ignite?
    Usually, the igniter or flame rod is dirty, broken, or out of position. Cleaning or replacing these parts usually fixes it.
  • Is ignition failure dangerous?
    Modern tankless heaters shut down automatically for safety, but you should never ignore gas smells or persistent error codes.
  • Can hard water cause ignition issues?
    Yes. Scale buildup can block water flow, triggering safety shut-offs. Regular descaling helps avoid this problem.
  • How long should a tankless heater last?
    Most units last 12–20 years with regular care, including flushing and filter cleaning.
  • Should I try to fix it myself?
    Simple checks are fine for most people. For anything involving gas, wiring, or major parts, always consult a professional.

Conclusion

An ignition failure can be stressful, but most issues are easy to diagnose and fix if you know what to look for. Start with the basics—check gas, power, filters, and air flow. If you’re still stuck, don’t hesitate to call a pro. And if your heater is on its last legs, consider upgrading to a new, more efficient model for peace of mind and endless hot water. Take care of your tankless system and it’ll take care of you for many years to come.

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