Condensing Models: On-Demand Water Heater Service Handbook • 27
SER
VICE PR
OCEDURE
S
5.
During this step, DO NOT press the
“Increase” or “Decrease” button for
more than two seconds at a time.
Press and hold down the “MIN”
button on the computer board.
While holding down the “MIN”
button, press either the “Increase”
or “Decrease” button to increase or
decrease the manifold gas pressure,
respectively (Figure 8, page 18).
Refer to the manometer to verify
that pressure has been set to the
desired value.
6. After the gas pressure has been
set, deactivate the water heater,
remove the manometer tube, and
replace the port screw.
7. Verify proper operation.
Checking the
Overheat Cuto
ff
Fuse (OHCF)
1. Locate the white OHCF which wraps
around the heat exchanger. (See
Figure 15, page 27.)
2. Find the white clip at the end of
the two blue braided wires coming
from the OHCF. It is located on
the right-hand side of the heater.
(Figure 15.)
3. Unplug the connection.
4. Test resistance at the end of the
OHCF with an ohmmeter
(Figure 15). Resistance should
measure 1 ohm or less. If the
reading is 1 ohm or less, the OHCF
is still intact. Reconnect the plug.
If the resistance exceeds 1 ohm,
replace the OHCF (part 319143-
067). Replacing this part will require
you to remove the heat exchanger.
Follow the “Replacing the Heat
Exchanger” instructions which are
found in the “Service Procedures”
section. Inspect the heat exchanger
for any burn marks, hot spots,
cracks, etc.
5. Restore power and test the unit. Be
very cautious during this step; avoid
contact with electrical components
and wires.
Checking the Flow
Sensor
If the water heater is connected to
the water, gas, and power supplies
correctly, but the fan motor does not
initiate when water flows, then the
flow sensor may have failed. (It may
not be telling the PC Board to initiate.)
Tools and Materials:
●
Flashlight
●
Towels
The flow sensor (item 402, p. 70) is
located below the water control valve
at the cold inlet. (See Figure 16.) Its
flow rate is determined by an impeller
that spins as fluid runs through it.
To check the flow sensor,
1. Remove the flow sensor as
described in “Flow Sensor/Control
Valve Removal and Installation,”
page 55.
2. Blow into the inlet of the flow
sensor. Listen for a spinning
impeller. It should spin freely for
a few seconds. If it comes to rest
abruptly or doesn’t spin at all, it
should be inspected for blockage.
If you have a remote, you can check
for flow rate by turning on power
to the water heater. Push the
“Info” button three times. This will
display flow if the flow sensor is
working properly.
3. Test the flow sensor:
3.1 Rea ach the
fl
ow sensor
wires.
3.2
Turn power to the unit back
on. (GAS MUST STILL BE OFF.)
3.3
Blow into the
fl
ow sensor.
If the fan ini ates, the
fl
ow
sensor successfully read the
air
fl
ow and should now work
properly.
Figure 15. Overheat Cutoff Fuse
(OHCF).
Overheat
Cutoff
Fuse
(OHCF)
Overheat
Cutoff
Fuse
(OHCF)
Blue
Braided
Wires
White
Connector
Flow Control/
Sensor
Figure 16.
