Becoming familiar with how a tankless water heater normally operates may help to figure out what is wrong with it. Assuming it is properly installed with appropriate gas, water, and electric connections, the following is how it should operate:
a. A hot water tap is opened enough that the flow sensor detects a flow rate through the heater greater than the activation point of 0.75 gpm.
b. The fan activates after flow is detected.
c. The computer checks for any problems with the unit before startup.
d. Igniter activates. You can hear the buzzing of the spark igniter.
e. Main gas valve, proportional valve, and solenoid gas valves will open. You will hear a deep “clunk clunk” noise.
f. Once a flame is detected, the red LED located on the computer board will activate.
g. In a multi?heater setup, the controller will activate the next heater in 2?4 gpm increments, depending on the set temperature.
a. The proportional gas valve will modulate based on the amount of hot water demanded and the temperature rise needed. The fan speed will modulate as well to create an efficient burn.
b. You will notice that only partial sections of the burner will be lit. This is normal operation; there are three sections on the burner assembly, and the computer controls the amount of sections needed based on the flow rate and temperature rise required.
a. The heater will shut down when the water flow rate drops below the deactivation point of 0.4 gpm.
b. The heater will close the main gas valve and solenoid gas valves, extinguishing the flame.
c. When the flame disappears the red LED will turn off.
d. The fan will increase in speed to purge the venting of any remaining exhaust gases. The length of post?purge can last up to 1 1?2 minutes.
e. The heater goes into standby waiting for the process to begin again.