Ensure the Takagi water heater is properly connected to a working power supply and is turned on, if the water heater is not working. Open the front access panel and press the test button, located on the black GFCI panel. A red LED light should turn on. If not, check and replace the local fuse or circuit breaker. Look to make sure the gas valve is completely open if the water heater is gas-powered.
Turn off the cold supply and open the hot pressure valve if the water flow is reduced, or the water temperature is fluctuating. Open the front access panel and pull out the filter. Remove excess dirt or debris and re-install the filter to the unit. Close the front access panel and close the pressure valve. Turn on the cold supply valve.
Locate the "Hi Limit" switch if the unit is not functioning properly. The switch is located at the upper left-hand corner of the heat exchanger, and looks like a small round black button. If the center button has popped out, push the center button back in.
Ensure the vents on all sides of the Takagi water heater are free of any obstructions, including furniture, drapes, toys or other objects, if the temperature is fluctuating or not working properly. Wipe the vents clean with a damp cloth.
Contact an authorized service technician if the above steps do not resolve the problem.