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3. NORMAL OPERATION
The 910 / 910 ASME (T‐M50 / T‐M50 ASME) is a combination of two tankless water heaters in one case,
as pictured below. When troubleshooting this unit, it is important to identify which major assembly, left
or right, is the side that the problem is located. Once it is determined which side contains the problem,
unless specifically stated, the procedures for troubleshooting and maintenance are exactly the same for
both the left and right heat exchanger assemblies.
1) ACTIVATION
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 0.5
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.
2) OPERATION
a. The proportional gas valves 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 burners will be lit. This is normal operation;
there are three sections on the burner assemblies, and the computer controls the amount of
sections needed based on the flow rate and temperature rise required.
3) SHUTDOWN
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 ½ minutes.
e. The heater goes into standby waiting for the process to begin again.
Figure 2
*This diagram illustrates the tankless water
heater design concepts only and is not accurate
to the units description.
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Troubleshooting Guide
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