506303-01 Page 33 of 40Issue 0938
System Sentry™ CONTROL DIAGNOSTICS
Troubleshooting
Make the following visual checks before troubleshooting:
1. Check to see that the power to the furnace and the
integrated ignition/blower control board is ON.
2. The manual shutoff valves in the gas line to the furnace
must be open.
3. Make sure all wiring connections are secure.
4. Review the Sequence of Operation (see page 27).
Start the system by setting thermostat above room
temperature. Observe system response. Then use the
information provided in this section to check the system
operation.
The furnace has a built-in, self-diagnostic capability. If a
system problem occurs, a fault code is shown by a red LED
on the control board. The control continuously monitors its
own operation and the operation of the system. If a failure
occurs, the LED will indicate the failure code. The flash
codes are presented in Table 5.
Fault Code History Button
The control stores the last five fault codes in memory. A
pushbutton switch is located on the control (see Figure 44 on
page 35 or Figure 46 on page 37). When the pushbutton
switch is pressed and released, the control flashes the stored
fault codes. The most recent fault code is flashed first; the
oldest fault code is flashed last. To clear the fault code history,
press and hold the pushbutton switch in for more than 5
seconds before releasing.
High Heat State LED
On these models, a green LED is provided on the control
board to indicate high heat state (see Table 6).
CFM LED (G2D95CT/U Models Only)
On G2D95CT/U models, an amber LED is provided on the
control board to display CFM. To determine what CFM the
motor is delivering at any time, count the number of times
the amber LED flashes. Each flash signifies 100 CFM; count
the flashes and multiply by 100 to determine the actual CFM
delivered (for example: 10 flashes x 100 = 1000 CFM).
High Heat State – Green LED
Table 6
LED
Status
Description
LED Off
LED On
High heat demand, high pressure
switch not closed
LED Flashing
High heat demand, operating
normally
No demand for high heat
Failure Codes – Red LED
Table 5
LED
Status
Fault Description
LED Off
LED On
1 Flash
2 Flashes
3 Flashes
4 Flashes
5 Flashes
6 Flashes
7 Flashes
8 Flashes
9 Flashes
No power to control or control
hardware fault detedted
Normal operation
Flame present with gas valve off
Pressure switch closed with inducer off
Low-fire pressure, rollout, drain
pressure, or aux limit open
High limit switch open
Not used
Pressure switch cycle lockout
Lockout due to no ignition
Lockout due to too many flame dropouts
Incorrect polarity and phasing
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