69-0845—2
15
S8910U UNIVERSAL HOT SURFACE IGNITION MODULE
4. The ignition module cannot be repaired. If it
malfunctions, replace it.
5. Only trained, experienced service technicians
should service hot surface ignition systems.
6. After servicing, verify proper system operation.
Perform the checkout steps in the Startup and Checkout
section as the first step in troubleshooting. Then check the
troubleshooting sequence (Fig. 8) to pinpoint the cause of
the problem.
After troubleshooting, perform the checkout procedure
again to be sure the system is operating normally.
Status LED used to Troubleshoot
The LED can be used to check the appliance status. A
description of the LED signals follows.
IMPORTANT
The LED shows system status for the current call
for heat. When the call for heat is interrupted
(thermostat satisfied or system power switched
off), the LED goes off and the status information
is lost.
•
Pulsing
heartbeat is the normal operating mode during
a call for heat (24V terminal is powered). The system
can be in any of the normal operating modes including
prepurge, warmup, ignition trial, between trial purge, or
normal run.
•
One flash indicates the S8910U is in an ignition lockout
mode. The most probable cause is the main burner
failing to light or failure to detect the flame. Run the
appliance through a call for heat and if the burner does
not light, check the:
—
gas supply
—
input voltage
—
hot surface igniter
—
gas control
—
wiring
If the main burner lights, but goes out at the end of ignition
trial, check the:
—
igniter/sensor
—
flame rod
—
burner ground connections
—
wiring
•
Two flashes indicates the flame rectification signal is
weak. The most probable causes are:
—
contaminated or mislocated igniter/sensor or
flame rod
—
poor flame sense leadwire insulation or
connections
—
poor gas pressure
If the flame rectification signal is strong when the appliance
lights, but weak while heat is being delivered, check for
overheating of the igniter/sensor, flame rod ceramic or
flame sense leadwires.
•
Three flashes indicate an internal error. The most
probable cause is an S8910U logic failure. Start a new
call for heat and if the three-flash signal returns, replace
the S8910U.
Ignition System Checks
Step 1:
Check the igniter wire harness.
Make sure:
a. Ignition cable does not run in contact with any metal
surfaces.
b. Connections to the ignition module and to the igniter
or igniter-sensor are clean and tight.
c. Ignition cable provides good electrical continuity.
Step 2:
Check the ignition system grounding. Nuisance
shutdowns are often caused by a poor or erratic
ground.
a. A common ground is required for the module,
igniter, flame sensor and main burner.
•
Check for good metal-to-metal contact
between the igniter bracket and the main
burner.
•
Check the ground path from the GND
(BURNER) terminal on the module to the
main burner. Make sure the connections are
clean and tight. If the wire is damaged or
deteriorated, replace it by following the
appliance manufacturer instructions. A
temporary leadwire connection between the
GND (BURNER) terminal and the main burner
can help confirm a ground path problem.
•
Check the temperature at the igniter ceramic
or flame sensor insulator. Excessive tempera-
ture permits leakage to ground. Contact the
appliance manufacturer if the temperature
exceeds the rating of the igniter or sensor.
•
If the flame sensor or bracket is bent out of
position, restore to the correct position.
•
Replace the igniter and sensor or igniter-
sensor with an identical unit if the insulator is
cracked.
STEP 3:
Check the flame sensing circuit.
a. Make sure the burner flame is capable of providing a
good rectification signal. See Fig. 6.
b. Make sure about 3/4 to 1 in. of the flame sensor or
igniter-sensor is continuously immersed in the flame
for the best flame signal. See Fig. 6.
c. Check for excessive (higher than 1000
°
F [538
°
C])
temperature at the ceramic insulator on the flame
sensor. Excessive temperature can cause a short to
ground.
d. Check for a cracked igniter-sensor or a sensor
ceramic insulator, which can cause short to ground,
and replace unit if necessary.
•
Make sure the electrical connections are clean
and tight. Replace damaged wire with
moisture-resistant No. 18 wire rated for
continuous duty up to 221
°
F (105
°
C).
e. If the igniter is other than a Norton 201 or 271, make
sure it meets the following specifications:
•
Igniter must reach 1832
°
F (1000
°
C) within
34-seconds with 102 Vac applied.
•
Igniter must maintain at least 500M ohm
insulation resistance between the igniter
leadwires and the igniter mounting bracket.
•
Igniter must not develop an insulating layer on
its surface (over time) that would prevent
flame sensing.
•
Igniter surface area immersed in flame must
not exceed one-fourth of the grounded area
immersed in flame. This would prevent flame
sensing.
•
Igniter current draw at 132 Vac must not
exceed 5A.