A.O. Smith ATI-140H-N, Service Handbook

Page: 30 / 76

30 • Condensing Models: On-Demand Water Heater Service Handbook
SER
VICE PR
OCEDURE
S
Before you begin these procedures,
consider removing the “Components”
section from this manual. It starts on
page 35.
This will allow you to lay the loose
pages beside this manual for easier
reference.
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 o
ff at the circuit
breaker, as appropriate.
1.2 Shut o ff the gas supply at
the gas supply line’s manual
shuto
ff valve.
1.3 Once the power and gas
have been turned o
ff ,
remove the front panel from
the water heater.
2. Remove the computer board from
the water heater according to the
following steps. (See also Figure
24, page 35.)
2.1 Unplug the wire connectors
for the high limit switch
(item 466, p. 70) and
exhaust thermistor (item
715, p. 70). See also
Figure 24, page 35.
NOTE: Outdoor models
will not include an exhaust
thermistor. Its loca on on
indoor models is shown on
Figure 24, page 35.
2.2 Unclip the high limit wires
from the side of the fuse
box assembly. The wires are
secured by a nylon clamp
(item 712, p. 68). See
also Figure 24, page 35.
2.3 Remove the following from
the front of the burner:
•
Flame rod wire (orange):
Item 708 (page 69);
See also page 35,
Figure 24.
•
Air-fuel ratio rod/AFR
wire (yellow):
See Figure 19.
See also page 35,
Figure 24.
•
Igniter rod wire (black):
Item 709, page 69;
See also page 35,
Figure 24.
2.4 Remove the screw that
secures the computer board
assembly. (See Figure 24,
p. 35.)
Do not remove
connectors from the circuit
board.
2.5 Remove the computer board
assembly.
3. Unplug both white connectors
above the fuse box (yellow wires),
then move the fuse box away
from the work area.
4. Remove the Gas Valve and
Manifold Plate Assembly:
4.1 Remove the screws that
secure the green ground
wires to the manifold plate.
4.2 Remove the screws that
secure the manifold plate
(Figure 24, page 35).
IMPORTANT: Remove only
the screws along the outside
edges of the manifold plate.
See Figure 21, page 31.
•
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.
4.3 Remove the screw on the
le side of the gas valve that
secures the power cord.
4.4 Disconnect the clear air
tube o
ff the le side of the
gas valve. (If necessary, see
Figure 37, page 42)
4.5 Disconnect the connector
on the right side (blue wires)
which goes to the overheat
cuto
ff fuse (Figure 24, page
35).
Solenoid (SV3)
Terminals
M
anif
old
Plate
Manifold
Plate
Figure 20.
Flame Rod Wire Connector:
To remove, pinch flat sides at end
with your finger nails, then slide
connector off the spade.
Figure 19.