How to Repair Ignition Failure on Tankless Water Heaters

Either you own a Rinnai tankless water heater, Navien, AO Smith, Takagi, Bosch or any other on-demand model, use this article and get the necessary information on how to deal with the problem “ignition failure”, which is the main reason why users complain about the flame loss, water heater not working, no hot water and alike.

The troubleshooting guide applies to tankless heaters with the electric ignition which is trying to light but unsuccessfully. 

Before going into details, let’s see first how does the tankless water heater work, what are the main components, and what is recommended to do/check, before troubleshooting.

How does the tankless water heater work?

The tankless water heater is the device that heats the water on demand. On-demand means that there is no storage water tank; water is heated while it is passing through the heat exchanger. The heat exchanger is located in the combustion chamber where the main gas burner with the ignition is also placed (below). The gas is coming from the gas supply, through the gas line and gas valve.

When the user opens the hot water tap, the electronics in the tankless unit reacts, allowing the ignition to start, generating the sparks. With the ignition electrodes creating sparks, the gas starts flowing into the combustion chamber, where it ignites the burner. 

Next, the water is heated, and the products of combustion are vented out. The water heater is running until the hot water tap is open.

This is a simple explanation of the tankless work and components involved.

Like other devices, the tankless water heater also has problems.

One of them is the ignition failure and flame loss.

As most of the newer advanced tankless water heaters utilize the self-diagnostic system and are equipped with the LCD display on the unit or remote controller, a numerical error code will display, or flashing light. 

Here are the ignition failure codes found on some tankless brands:

Takagi – Error Code 111, 11 or 3

Rinnai – Error Code 11

Navien – Error Code E003

Noritz – Error Code 11

The ignition failure on tankless water heaters can occur to any brand and model, no matter how advanced or not is. The failure can be caused by a problem inside the water heater or due to an external cause.

But, before trying to fix the unit, let’s go first through the troubleshooting checklist, recommended by the manufacturers. The checklist can assist you in fixing some common and frequent problems, such as flame loss, no hot water, ignition problems, or avoid potential issues:

  • Make sure that gas and water are open and electricity is ON (120 VAC supply).
  • Confirm that the right gas type (natural gas or LP) is used.
  • Make sure the pressure is per specs.
  • Verify that all air was purged from the gas line and after the installation.
  • Make sure plumbing is installed correctly, per codes and manufacturer’s instructions.
  • See is the water pressure per specs.
  • Make sure that water is not too hard (over 7 grains) as it can cause sediment build-up.
  • If your location is at the higher altitude check out is the water heater properly set or is it designed for that.
  • And finally, is there an error code?

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Troubleshooting ignition failure problem

Some brands of tankless water heaters are set in a way that if there are three failed attempts to ignite the burner, the error code will appear showing the ignition failure problem.

Here are the reasons, symptoms, and solutions for the ignition problem: 

  • Hi-limit switch has tripped. Turn the unit off. Try to reset it. Turn the power back on. If the unit fires, the problem is with the switch and should be replaced (but first check out the cause).
  • Gas supply. Check if there is an interruption in gas delivery, is the pressure reduced or the gas quality is low – it might not be free of debris. Or, maybe the gas pipe still has some air that needs to be purged. Check the water heaters rating plate for the proper gas pressure. If the minimum inlet pressure is not present, the unit might not ignite.
  • Gas connection. Check gas connections to the heater and from the gas control valve to the combustion chamber. If there is moisture in the connecting tube, the gas valve needs to be replaced.
  • Water/moisture. Check the burner and heat exchanger for corrosion due to excessive moisture. Also, inspect all the wiring and electrical connections that could be wet. The reason for the moisture could be a leak from the heat exchanger or other components, or improper venting and condensation.
  • Condensate drain. Is the condensate drain installed? Is there a blockage? 
  • Gas type. Is the right gas type used? Did you do the gas conversion? If the tankless water heater was set to use different gas type instead factory set, check if the DIP switch on the PC board is set to the right position.
  • Overheat cutoff fuse. See is the overheat cutoff fuse damaged.
  • Dirty electrodes. Clean the dirty flame sensor and igniter if the flame goes out after a second or two of being on. If you see carbon or a white substance build-up, clean it, but first remove them from its brackets. Be gentle while cleaning the electrodes because it can be easily damaged or out of position. Use the 100 grit sandpaper or similar.
  • No sparks. The proper spark remains steady and is in place. The weak spark jumps around. If the spark is weak or there is no spark at all, check that the igniter wire connection is in place and secured.
  • Loose wire connection. Make sure that the wire connection at the ignition rod is securely tight, and at the PC board too.
  • Flame rod. Some models have multiple flame rods, so make sure they are correctly installed with the correct wiring. The flame rod must be touching the flame when the unit fires.
  • Loose electrode/flame rod. Make sure that the spark electrode and flame rod are installed tight in its brackets and in the correct position. If replacing, make sure to use the new gasket. A loose element can drop and touch the metal burner creating a short. Check if there are damages on the ceramic insulator of the electrode.
  • Venting. Vent blockage is the frequent cause of ignition failure. Anything blocking the exhaust or air intake should be removed. Also, look for the loose connections, and are the vent type, bends, lengths and clearances per specs. If there is incomplete combustion caused by the recirculation of exhaust gases, it will result in carbon build-up on the flame rod. 
  • Burner. Inspect the gas burner for debris or condensate build-up and if necessary use the air compressor or strong vacuum cleaner to clean. Debris and condensate could prevent the burner from firing or cause the inside turbulence.
  • Altitude. Make sure to follow the instruction from the model installation guide on how to set the dip switch and manifold gas pressure when installing the water heater at the higher altitude.
  • The problem with the gas valve – moist, debris, mechanical issues, malfunction.
  • Faulty electronic board – incorrect voltage, bad connections, malfunction.

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Testing the igniter

Turn the gas supply to the water heater off. Unplug the igniter wire. Use the insulated pliers, hold the igniter wire and ¼” from a metal part. Run the heater. If there is no spark than fix one of the following problems:

  • Loose connections
  • Damaged component
  • Low voltage on the PC board
  • Broken PC board


As can be seen from the above troubleshooting guide, ignition failure problem shouldn’t be hard to fix, as long as you have some basic knowledge about electricity, gas, and plumbing systems.

And remember, if you don’t feel comfortable about fixing the tankless water heater, you can always contact the professional or have them call you (just fill out this form for contact).

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