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6. MAINTENANCE
Safety is the most important part of this guide. These
procedures must be done by a licensed competent
technician. AO Smith is not liable for the actions of the
technician if he/she fails to adhere to any or all safety
procedures, specifically in regards to electrical and gas
safety.
The 910 / 910 ASME (T‐M50 / T‐M50 ASME) is a
combination of two tankless water heaters in one case.
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 maintenance are exactly the same for both
the left and right heat exchanger assemblies.
a. TOOLS ‐ Gather the following materials together: Sheet of 100 Grit Sandpaper, #2 Philips Screw
Driver, Flashlight
2) POWER ‐ Disconnect power to your unit by either unplugging it from the wall outlet, or by the circuit
breaker, depending on the setup. Press the GFI 'TEST (OFF)' button; if the red light does not come
on, power is successfully disconnected.
3) FRONT COVER ‐ Remove the front cover.
4) ROD ASSEMBLY –
a. Locate the black, yellow, and orange wires located in the
center of the unit.
b. Remove the three Phillips head screws holding the panel in
place.
c. Pull the assembly out. Do not lose the circular window.
5) SENSORS – It is important to be very gentle with the sensor rods while cleaning them, as they will
easily bend out of place. Their original position relative to the burner needs to be unaltered to
function properly.
a. Clean the flame sensor with 100 grit sandpaper, thoroughly to a bright finish.
b. Clean the air fuel ratio rod with 100 grit sandpaper, thoroughly to a bright finish.
6) REASSEMBLE ‐ Reassemble the unit in reverse order – sight glass, gasket, rods, and metal cover. Key
points to remember:
a. Connect all 3 wires on front of burner.
b. Inspect all of the gaskets.
c. Be sure the circular burner window is still in place.
CLEANING THE ROD ASSEMBLY
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Troubleshooting Guide
Figure 25
Rod Assembly
Figure 26
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