Takagi T-H3J-DV, Service Handbook

Page: 19 / 80

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On-Demand Water Heater Service Handbook for 240, 340 & 540 Condensing Models • 19
the black and red wires. (See page
30 or 31.) Normal voltage range
(black-red):
7 VDC - 16 VDC. If the voltage is out
of range, replace the computer board.
(See page 49 or 50.)
Code 661: Bypass valve fault
(540 (T-H3) model only)
This code indicates a bypass valve fault.
1. Inspect the bypass valve (item number
403) for the following:
•
Broken or disconnected wires
(Be sure to look behind the fuse box
and check the wire assembly from
the bypass valve. Wire colors: red,
yellow, white, blue, brown.)
•
Locked motor drive due to debris
or scale build up inside the valve
assembly
•
Water leakage at the bypass valve
Check the resistance of the bypass
valve. To check it,
a.) turn off electrical power to the
water heater, then b.) unplug the
bypass valve’s harness. There is a
connector in the middle of the harness
which you can access by removing the
computer board. (See Figure 41, page
49. The harness’ wire colors are red,
yellow, white, blue, brown).
c.) Check the resistance between the
brown and red wires. (You can use the
pins in the female connector.) Normal
resistance (brown-red): 50 to 85 Ω. If
the resistance is out of range, replace
the bypass valve.
2. Check the voltage of the bypass valve.
To check it, measure between the
brown and red wires. (See page 31.)
Normal voltage range (brown-red):
3 VDC - 11 VDC. If the voltage is out
of range, replace the computer board.
(See page 50.)
Code 701: Computer Board
Fault / Proportional Gas Valve
Fault
This code indicates a computer board or
proportional gas valve fault.
1. Verify that the red/white harness is
connected at both the proportional
valve solenoid and the computer
board (PCB).
2. Inspect the computer board (PCB)
for connection/breakage of wires
and/or burn marks.
3. Check the operation of the outlet
thermistor as follows:
3.1 Push the on/off button on
the temperature controller
or remote controller so the
orange STAND BY LED turns
off.
3.2 Run water through the
heater.
3.3 Check the reading of
the outlet thermistor by
pushing the INFO button on
the temperature/remote
controller two times.
Compare it to the inlet
thermistor. The readings
should be similar and it
should be reading the
temperature of the supply
water. If there is a difference
of more than five degrees,
refer to “Code 311, 321, 331
or 341: Thermistor Failure”
on page 16.
When you are finished,
retest the water heater.
4. Check the proportional gas valve
as described in the following sub-
steps. The proportional valve is
located at the bottom of the gas
valve assembly and has red and
white wires connected to it.
4.1 Turn off the power supply.
4.2 Check the wire connections
at both the gas valve and
on the control board. Make
sure that they are secure
and free of burns or cuts.
4.3 Check the resistance across
the proportional valve (red,
white wires). Normal value
is 20-40 Ω . If the resistance
is outside of this range,
replace the gas valve. If
you do replace the gas
valve, verify that the gas
supply pressure is within
specifications.
Code 711: High Limit Switch /
Overheat Cutoff Fuse Circuit is
Compromised
When power is turned on to the
heater, the computer performs a
diagnostic check of the gas valve,
high limit, and Overheat Cutoff Fuse
(OHCF) circuits. If any of these are
compromised, this code will appear.
1. Inspect the dark blue common wire
to the high limit switch, the OHCF,
and the gas valves for any breaks
or cuts.
2. Verify proper wiring harness
connections to the gas valve
solenoids. (For each connector,
the number stamped on the metal
must match the number that is
printed on the wire’s label. See
Figure 6, page 17.)
3. Check the High Limit switch. Refer
to “Code 111 or 121: Ignition
Failure / Flame Loss,” page 14.
4. The Overheat Cutoff switch may be
compromised. Refer to “Checking
the Overheat Cutoff Fuse (OHCF),”