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Part number 550-142-054/0411
77
GV90+ gas-fired water boiler — Boiler Manual
c. Immediately disconnect the return temperature sensor plug from
the IBC.
d. Measure the resistance of the sensor. Write down the result.
e. Let the sensor cool to room temperature and measure the resistance
again. Write down the result.
f. Compare the sensor resistances at both temperatures to the closest
temperatures in Figure 91.
g. If the measured values are within 10% of the values listed, the sen-
sor is good. If not, replace the sensor. See Replacement parts for
the part number.
3. Fixed resistor method
a. With the boiler power OFF, disconnect the return temperature
sensor plug at the IBC.
b. Insert a 2500-ohm resistor into the IBC sensor plug.
c. Restart the boiler.
d. If the boiler operates with the resistor, but not with the sensor, try
replacing the sensor. See Replacement parts for the part number.
IBC (integrated boiler control)
Make sure ground wiring is installed per wiring diagram. Good grounding
is extremely important for proper operation.
Solder or water splatter between plugs and circuit board
can cause improper operation of IBC. Place a shield over the
boiler internal controls and components during installation.
Failure to comply could result in severe personal injury, death
or substantial property damage.
IBC indicator lights — lockout modes
• See Charts 1 through 8 in this section for detailed trouble-shooting
procedures.
• To reset control after a lockout, turn off power at the 120 VAC service
switch or turn down all thermostats. Wait 45 seconds. Then restore
power and call for heat.
• After an over-temperature lockout (POWER and LIMIT lights flash-
ing), the control will only reset after interruption of 120 VAC for 45
seconds. (And temperature at return water temperature sensor must
be below 240°F.)
POWER light flashing alone
• Usually indicates reversed polarity of 120 VAC power wires.
POWER and TSTAT CIRC lights flashing
• Usually indicates stray voltage on external thermostat circuit wires
or return water temperature entering boiler sections has not reached
140°F within 20 minutes.
POWER and LIMIT light flashing alternately
• Usually indicates that limit circuit failed to cut off boiler at high tem-
perature — return water temperature sensor has sensed water over
235°F.
POWER and PRESS SWITCH lights flashing
• Usually indicates pressure switch is closed when it should not be, or
pressure switch failed to close within 5 minutes of blower starting.
Troubleshooting (continued)
Figure 91 Return temperature sensor resistance
Temperature
°F
Resistance
Ohms
Temperature
°F
Resistance
Ohms
60 15300 140 2480
70 11900 160 1680
80 9310 180 1160
100 5840 200 810
120 3760 212 674
Figure 92 GV90+ Integrated Boiler Control (IBC)
POWER and FLAME lights flashing
• Usually indicates control has had three unsuccessful
ignition attempts or sensed flame when it shouldn’t
be there. Boiler may not be properly grounded.
IBC indicator lights —
non-lockout modes
TSTAT CIRC light flashing alone
• Usually indicates return water temperature sensor
detects water at boiler return pipe less than 40°F.
Both internal circulators will run continuously,
even with no call for heat, until temperature rises.
LIMIT light flashing alone
• Usually indicates an open or shorted return water
temperature sensor.
Troubleshooting the IBC
• See Figure 93, page 78 for location of harness plug
receptacles and plugs on the IBC.