Condensing Models: On-Demand Water Heater Service Handbook • 37
MAINTENANCE
Replacing the Heat
Exchanger (Indoor
Models)
Tools:
#2 Phillips Screw Driver, 8” long
(a magnetic tip is helpful)
WARNING!
□
Disconnect power by opening
the circuit breaker or removing
the fuses before installing or
servicing.
□
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.
Consider removing the following
sections from this manual for easy
reference:
•
“Component Diagrams/Item
Numbers” (starting on page 67).
•
Figure 24, page 35, which shows
the location of basic components.
This will allow you to lay the loose
pages beside this manual for easier
reference.
Also, screw sizes vary. We recommend
bagging and labeling screws as you
remove them, or reinstall them in their
proper places as you proceed with
disassembly. This will make
reassembly easier.
Removing Heat
Exchanger Components
(Indoor Models)
1. Shut the unit down as follows:
1.1 Shut
O
ff
power and gas
supply as follows:
1.1.1 Shut o
ff
Power by
disconnec ng the power
cord or shu ng o
ff
the
power disconnect.
1.1.2 Shut o
ff
the gas supply to the
water heater at the manual
gas shuto
ff
valve.
1.2
Drain the water from the
heater as follows:
1.2.1 Close the shuto
ff
valves on
the hot and cold side of the
heater.
1.2.2 IF isola on valves are
installed: open up the drain
ports.
1.2.3 IF isola on valves are not
installed: remove the
fi
lter
(item 405, page 70) and
open the pressure relief
valve.
2. Remove the Temperature
Controller (item 721, page
67) by disconnec ng the
white connectors that go to the
computer board.
3. Remove the computer board as
follows (item 701, page 68; see
also Figure 24, page 35):
CAUTION:
•
During the next step, consider
taking a digital photo to aid in
reassembly.
•
Do not touch the circuit board
components. Doing so may
cause damage by electrostatic
discharge.
3.1
Disconnect all wire
connectors from the
computer board.
3.2
Remove the screw at the
top of the computer board
assembly, then remove the
board (Figure 24, p. 35).
4. Remove the fuse box assembly
(items 703, 120; page 68):
4.1
Disconnect the connector at
the top port which comes
from the main power supply.
4.2
Disconnect the freeze
protec on heater wires.
There are 6 sets of white
connectors with yellow wires
(two above the assembly,
three below the assembly,
and one below the secondary
heat exchanger on the right
side).
4.3
Remove the screw that
secures the fuse box and li
the fuse box away.
5. Remove the
fl
ow sensor/control
valve (item 402, page 70; see
also Figure 24, page 35):
5.1
Remove fasteners 16A and
14-22 (items 458 and 459,
page 70).
5.2
Pull the cold connec on
tube (item 462, p. 70)
from the outlet of the
fl
ow
sensor/control valve and
li the valve o
ff
of the inlet
connec on. You may have to
twist the valve o
ff
of the inlet
connec on.
6. Remove the cold connec on tube
(item 462, page 70) as follows:
