Water Is Too Hot; Temperature Fluctuates When A Fixture Is Opened - A.O. Smith ATI-140H-N Service Handbook

resides in the plumbing line,
not in the tankless unit.
•
Check for crossed plumbing between
cold water lines and hot water lines.
See the "Service Procedures" section
for instructions.
•
Unit may be hard water scaled.
The scale acts as an insulator
preventing the heat exchanger
from transferring heat to the
water. Refer to "Descaling the
Unit," page 29.
•
The unit may not be receiving
enough gas.
◦
The gas supply valve may not
be fully open.
◦
The gas line may be sized
improperly.
◦
The gas supply pressure
may be too low. This may be
caused by a malfunctioning
gas supply regulator, so
check to see if the regulator
is working properly. See
"Check gas supply" later in
this section.
•
If a recirculation system is
installed, ensure that a check
valve is installed between
the pump discharge and the
connection to the cold water
supply. Inspect the check valve
for proper operation. If there
isn't one installed, or if it is
malfunctioning, cold water may
be back-feeding into the system.
•
If a mixing valve is installed, check
to see if it is operating properly
and not allowing water to cross
over.
•
A 101 error code will reduce the
amount of gas input into the
heater. If the heater is displaying
a 101 error code, see "Abnormal
Combustion" on page 12.
8 • Condensing Models: On-Demand Water Heater Service Handbook
•
Output temperature will be
affected if air flow is impeded.
◦
Check for construction dust
and debris in venting, such as
dry wall dust.
◦
If there is dust inside the
cabinet, there will also be
dust inside the burner and
heat exchanger. Refer to
"Cleaning the Combustion
Components," page 29.

Water is too hot.

•
The temperature setting
may be set too high. Adjust
the temperature using the
temperature controller or the
remote controller.
•
The flow adjustment valve could
be obstructed due to hard water
scale or debris, causing lower than
expected water flow. Verify water
flow with a graduated container
or with the remote temperature
controller, if one is installed.
•
The output thermistor could be
compromised. This component
may be checked by entering
the Diagnostics Mode on the
remote controller or temperature
controller. Turn power off to the
unit and run cold water through
it; check to see if the inlet and
outlet temperatures read the
same on the remote. Press the
INFO button once on the temp/
remote controller. The inlet water
temperature will be displayed.
Press the INFO button again to
show the outlet temperature. If
the readings are not similar, then
one of the thermistors may not
be reading correctly. Refer to
error codes 311 and 321 in "Error
and Flash Codes" (p. 10).
Temperature fl uctuates when a
fi xture is opened.
Make sure that the unit is installed
properly.
•
Test whether the problem is
within the unit or external to the
unit (i.e., plumbing system).
•
Plumbing connections:
1. Check for a crossed
connection. See "Checking
for a Crossed Connection,"
page 25.
2. Problems with the
recirculation system:
◦
Make sure that a
check valve is installed
between the pump
discharge and the
connection to the cold
water supply.
◦
Check to see if the pump
is operating properly.
◦
Check for air cavitation.
If present, the pump
will be very hot or
chattering.
◦
Check the directional
indicator on the pump
flange.
◦
Check the sizing of the
pump. A minimum flow
of 2 gpm is required.
•
Check gas supply:
◦
Verify that the gas meter
is capable of supplying
sufficient gas supply to all
gas appliances. Determine
the sum of all gas appliances'
maximum energy input (in
cubic feet per hour). This
number must be less than
the maximum ratings shown
on the gas meter's rating