Takagi 100 Series, Service Handbook

Page: 8 / 80

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8 • On-Demand Water Heater Service Handbook for 240, 340 & 540 Condensing Models
Next Step:
Finally, check to see if the unit has an error
code. The error code will be displayed on
the temperature controller (or remote
controller) and by flash codes on the
green LED on the computer board. See
Figure 3, page 11. See also the error
code chart on page 11.
•
If it is displaying an error code, proceed
to Error Codes, p. 11.
•
If there is no error code, proceed
to “General Issues.”
General Issues
Proceed to the “Error Codes” section
if an error code is identified. For other
common problems that do not involve
error codes, see if the following items
help:
Water is not hot enough.
•
What is the set temperature of
the heater? Temperature can be
adjusted using the temperature or
remote controller.
◦
Isolate the heater by closing
the hot isolation valve. Open
the hot drain valve and test
the heater. A hose may need
to be connected to the hot
drain prior to opening it in
order to drain the water
properly.
◦
If the temperature and flow
rate are correct through the
drain, then the problem
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” on page 38.
•
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.
•
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 39.
Water is too hot.
•
The temperature setting
may be set too high. Adjust
the temperature using the
temperature controller or the
remote controller.
•
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
On-Demand
Water
Heater
H C
A
B
C D
Outlet Hose
(Hot)
Bucket
“A” Open
“C” Closed
“B” Closed
“D” Open
Figure 2.