A.O. Smith 110 Troubleshooting Manual - page 31
Troubleshooting Guide
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Page
CHECKING THE FLOW SENSOR
If the tankless unit is properly connected to water, gas, and power supplies but the fan motor does not
initiate when water is run through it, the flow sensor is most likely not working properly and not telling
the PC Board to initiate.
1) TOOLS ‐ Gather the following materials together:
a.
Degreaser in a pump action bottle
b.
#2 Philips Screw Driver
c.
Flashlight
d.
Old Towels, at least three
2) PREPARE THE UNIT –
a.
Drain the unit by following the procedures on p. 21.
b.
Disconnect power to the unit.
3) FRONT COVER ‐ Remove the front cover.
4) COMPUTER BOARD
a.
Remove the screw holding the computer board to the
manifold, and let the computer board hang in front of the unit
b.
Disconnect the flow sensor wire.
5) DISCONNECT FROM WATERWAY
a.
The flow sensor is located behind the computer board.
b.
Remove the waterway clips on each side of the flow sensor by pushing on the tabs.
6) CHECKING THE FLOW SENSOR
a.
Check for functionality. Flow rate is determined by an impeller that spins as fluid runs through
it.
b.
Blow into the inlet of the flow sensor. Listen for the spinning impeller; it should spin freely for a
few seconds. If it comes to rest abruptly or doesn’t spin at all, it needs to be cleaned or
replaced.
c.
Place the flow sensor into a container of lemon juice or another degreaser for 30 minutes and
check the spinning capability again.
d.
Test the cleaned flow sensor by “jumping” the system:
i. Reattach the flow sensor wires.
ii. Turn power back on to the unit. (GAS SHOULD STILL BE OFF)
iii. Blow into the flow sensor; if the fan initiates, the flow sensor successfully read the
airflow and should now work properly.
7) REASSEMBLE ‐ Reassemble the unit in reverse order. Ensure that the O‐rings and waterway clips are
all in place.
Figure 34