Troubleshooting & Repair


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Takagi tankless heaters have proven themselves to be highly reliable over the years, requiring little maintenance or repair. However, a few minor service requirements should be performed at least once a year to insure trouble-free performance. These are outlined in your Service and Installation Manual under “Maintenance and Service.”


External Troubleshooting

A very high percentage of service problems requiring troubleshooting can usually be traced to causes external to the unit. These problems in order of occurrence are:
Improper Venting: The most common error is the use of normal B-vent, which can quickly destroy the heat exchanger due to acidic condensation. Improper venting is also unsafe. All Takagi tankless water heaters must use sealed stainless steel vent pipe approved for use in Category III appliances.
Gas Supply Line Problems: Undersized Line: There is a great tendency to just “hook up to the existing gas line,” which is usually only ½ inch diameter. As stated in the installation manual and in this guide, the minimum size is ¾ inch, but this size is good only for certain lengths from the source. Strict attention must be paid to the gas-line requirements section in the installation manual. Make sure that you size for the maximum BTU per hour rating and not the minimum.
Incorrect Gas Pressure: The working pressure should be from 5 to 10½ inches WC for Natural Gas and 9½ to 14 inches for Liquid Propane, depending on the model.
Wrong Type of Gas: Make sure that you order the correct heater for the type of gas you will be using, Natural Gas or Liquid Propane. There is no modification available to change the unit.
Water Flow/Temperature Fluctuation Problems: If there is a low flow from the heater, the first thing to check would be the input filter. Turn off the cold supply, relieve the hot pressure and remove the filter to check for debris. Clean or replace the filter and then check the flow again. If there is inadequate hot water or variations in temperature, check for plumbing “cross flow,” which means there is a connection somewhere between hot and cold. This may be as inconspicuous as a worn seal in a one-handle faucet. To check for this, shut off the cold supply to the heater and open either the pressure relief valve or any hot-water faucet. If there is a steady flow of water from the hot output after the pipe has drained, there is a cross flow somewhere that must be fixed.
Other causes of temperature fluctuations can be missing or incorrectly installed check valve, especially on multiple systems. The gas line may be too small, or the heater temperature may be set too high in an effort to “get more hot water.” This can cause a shower to be turned too far to the cold side, which doesn’t allow enough hot-water flow to keep the heater on steadily. In most circumstances, the heater should be set to its default of 122°F.
Hard Water Problems: In areas where the water is very hard with high levels of calcium and magnesium (about 9+ grains per gallon or 70 to 140 parts per million), Takagi recommends that the water be treated with a water softener or some other de-scaling device. Do not use a reverse osmosis process! It will destroy the heat exchanger. Removing minerals or keeping them in suspension will greatly lengthen the life of the heater and reduce service problems.
Environmental Issues: The heaters should be installed in relatively clean areas with access to combustion air that is free from dust, lint, grease, or chemicals. If any of these conditions are present, a direct vent model should be installed. For this reason, restaurant, beauty salon and industrial applications should always get a direct vent unit, which draws it combustion air from the outside.



Internal Troubleshooting and Repair

Internal troubleshooting should be done only after all of the above external criteria have been thoroughly checked and repaired. If the heater still does not work correctly, here are some basic steps to take with all Takagi models. A more in-depth troubleshooting guide is available in the Service and Installation Manual provided with the heater.
Remove the front cover.
Make sure there is AC power to the unit by pressing the test button on the black GFCI panel
The red LED should turn on. If it does not, check for power to the unit or blown fuses. Push the reset button. The LED will turn off and the unit should be ready to fire.
Make sure that there is gas supply to the unit. This should be done using a pressure gauge or by verification from the gas company.
Make sure there is good water flow. If there is not, check the filter, as described above under water flow problems. Check for reversed hot and cold lines. (Oops! Even licensed professional plumbers can make an occasional mistake.) Do you have adequate water pressure and flow? All units need 0.75 gallons per minute to activate, except the T-K3, which needs 0.5 GPM.
Check the following sequence of events after turning a hot water fixture on:
1. The fan turns on.
2. The igniter starts sparking or clicking.
3. The gas valves “clunk” as they open up.
4. A flame appears in the viewing window and the red “burner on” lamp lights up.
5. Adequate hot water starts flowing out of the unit in about 6 to 10 seconds. This timing applies to all Takagi models except the T-M1, which may take a few seconds longer.
If one of the above does not happen, use one of the following methods to determine the cause of the problem:
1. Check the hi-limit switch at the upper-left-hand corner of the heat exchanger. It is a small, black, round switch that may have a center button popped out slightly. This may have happened randomly, or it may be a sign that your heat exchanger is clogging up with deposits and needs to be flushed out. If resetting this switch causes the heater to run temporarily before the button pops out again, a service call is required.
2. Use your service manual’s “Common Troubleshooting” section to determine what is causing the problem. This section explains the meaning of the error codes, which are shown as flashing LED’s on the computer board or as numeric codes on a remote control. These error codes are also available on the Takagi Translator, a tool for selecting the proper Takagi model for any hot-water application.