Plumbing, Heating and Pool Repair Guides

Takagi TK-JR Tankless Water Heater Troubleshooting


WeT HeaD KnowledgeIf you are the proud owner of a Takagi TK-JR Tankless Water Heater and are having issues with your unit I’m sure you are discouraged and hesitant to hire a pricey technician to fix something that could be a simple fix. Good news, you’ve come to the right place! This troubleshooting and repair guide should hopefully assist you in quickly and easily solving whatever problem you have with your hot water heater. This guide should help you handle anything related to: water flow regulation problems, condensation, temperature issues, hard water and many other things. If you think that you may not be able to complete these repairs safely please don’t hesitate to call a professional technician.

PROBLEM: Condensation affecting the heat exchanger.

SOLUTION: The biggest cause of this problem is lack of ventilation. For this particular model of tank less water heater (and many others) it is imperative that only stainless steel vent pipe that is acceptable for use inCategory III appliances be used. These pipes must also be sealed in the correct fashion.

PROBLEM: Low gas pressure.

SOLUTION: This can be caused by gas lines that do not have a big enough diameter, the minimum size approved for use in this heater is 3/4 inch. The proper pressure should be from 5-10 1/2 inches WC for natural gas and for propane it is 9 1/2 to 14 inches.

PROBLEM: Fluctuation in water flow and temperature.

SOLUTION: If the water pressure is too low you should ensure that the input filter is clean and free of blockages. Another thing that could cause this is plumbing crossovers meaning that the hot and cold water supply are connected when they should not be. To test for a plumbing crossover you should shut off the cold water supply and disconnect the heater. Then open up a hot water release valve or turn on a sink faucet , if there is water flowing when this happens then you have a plumbing crossover. To troubleshoot a temperature issue you should first make sure that the gas lines are the correct size. Also, make sure that the temperature setting is not put up too high, this will cause the shower to overcompensate by turning the control too far to the cold side and in turn doesn’t allow enough hot water flow to keep the heater on.

PROBLEM: Hard water.

SOLUTION: Hard water usually occurs when the levels of calcium and magnesium are too high. If you are having problems with hard water try using a water softener or another product that does de-scaling. However, you should never use any process involving reverse osmosis because it will break the heat exchanger.

PROBLEM: Heat exchanger is malfunctioning.

SOLUTION: Make sure the hi-limit switch on the top left corner of the heat exchanger is working properly. If the center button is protruding it might mean that your heat exchanger is obstructed by mineral deposits. If this occurs you will need to drain and flush your water heater and refill it with chlorinated water.

PROBLEM: Water is not heating up.

SOLUTION: Check to see that the unit is getting power and that LED lights on the front panel come on. Then check the gas lines and take a pressure reading to ensure that the water heater is receiving the appropriate level. There could be water flow issues which would affect water temperature. Check to see if there are any obvious obstructions or if the filter is dirty. If you are still having trouble it could be due to hot and cold water supply being connected to the wrong sides of the unit. Also, make sure that your hot water heater is getting no less than 0.75 gallons per minute.


  1. sometimes the hot water runs out. is the unit too small for 2 condominiums with only 2 people in each unit?


  2. On vacation for 8 days when I returned went in house and turned on hot and cold water. Lots of noise sputtering water with rust color. eventually lines ran clear water. Shower head clogged but now workable.

    No hot water being produced. Might’ve run out of propane so filled tank up!

    No hot water still. ERROR CODE 11 flashing and buzzing sound coming from spark ignition. Ignitor not lighting!

    Help!! Please!!

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