Takagi T-H3J-DV, Service Handbook

Page: 56 / 80

MAINTENANCE
MAINTENANCE
56 • On-Demand Water Heater Service Handbook for 240, 340 & 540 Condensing Models
fasteners organized and will expedite
reassembly.
WARNING
□
Disconnect power to the water
heater by unplugging it from
the wall outlet or turning it
off at the circuit breaker, as
appropriate.
□
Use a non-contact circuit tester
to confirm that power is off
before working on or near any
electrical parts.
□
Ensure that the gas supply is
shut off at the manual gas
shutoff valve.
□
Replace the front cover after
servicing.
□
Failure to follow these warnings
can lead to personal injury or
death.
Gas Valve/Manifold Plate
Removal
1. Prepare the water heater for
service as follows:
1.1 Disconnect power to the
water heater by unplugging
it from the wall outlet or
turning it off at the circuit
breaker, as appropriate.
1.2 Shut off the gas supply at
the gas supply line’s manual
shutoff valve.
1.3 Once the power and gas
have been turned off,
remove the front panel from
the water heater.
INDOOR MODELS: Remove
the Temperature Controller
(item 722, page 71) by
disconnecting its white
connector from the
computer board.
2. Remove the computer board from
the water heater according to the
following steps. (See also Figure
41, p. 49 or Figure 42, p. 50.)
NOTICE:
Do not remove connectors from
the circuit board during the
following steps.
2.1 INDOOR MODELS ONLY:
Unplug the wire connectors
for the exhaust high limit
switch (item 472, p. 74)
and the exhaust thermistor
(item 718, p. 74). See also
Figure 41, page 49.
2.2 Disconnect these wires from
the front of the burner:
•
Flame rod wire (orange).
See Figure 41, p. 49
or Figure 42, p. 50
(center of picture).
•
Air-fuel ratio rod/AFR
wire (yellow). See Figure
41, p. 49 or Figure
42, p. 50 (center of
picture).
NOTICE: The yellow wire
is locked onto the rod’s
conductive spade. To
release the flame rod
connector, follow the
instructions in Figure 25,
page 37.
•
Igniter rod wire (black).
See Figure 41, p. 49
or Figure 42, p. 50
(center of picture).
2.3 Remove the screw that
secures the computer board
assembly.
See Figure 41
(p. 49) OR Figure 42 (p.
50).
Do not remove connectors
from the circuit board.
2.4 Remove the computer board
assembly.
3. Remove both screws which secure
the fuse box to the manifold plate.
Move the fuse box away from the
work area. See Figure 41 (p. 49)
OR Figure 42 (p. 50).
4. Unplug the white connector above
the main gas valve (yellow wires).
This connector is shown just above
the “Main Gas Valve” in Figure 41
(p. 49) and Figure 42 (p. 50).
5. Remove the Gas Valve and
Manifold Plate Assembly:
5.1 Remove the screw that
secures the remaining
ground wire (green) to the
manifold plate.
5.2 Remove the screws that
secure the manifold plate;
doing so will remove the
igniter assembly as well.
NOTICE: Remove only the
screws along the outside
edges of the manifold plate.
See Figure 48, p. 57.
•
DO NOT remove the
screws securing the
manifold plate to the gas
valve.
•
DO NOT remove the
screws along the interior
of the manifold plate.
5.3 INDOOR MODELS: Remove
the power cord mounting
tab. (Figure 41, page 49.)