Honeywell S8701 - Manual (Page 8)

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8
S8701/S8702 DIRECT SPARK IGNITION CONTROLS
6. Check the flame sensor and its mounting bracket.
Correct the position if bent out of shape.
7. Review the S8701/S8702 normal sequence of
operation. See START SYSTEM section.
S8701/S8702 COMPONENT CHECKS
Spark Ignition Circuit
The step-up transformer in the S8701/S8702 provides
spark ignition at 14,000 volts (open circuit). To check the
spark ignition circuit, proceed as follows:
1. Shut off gas supply to the gas control.
2. Disconnect the ignition cable at the S8701 or both
S8702 spark terminals to isolate the circuit from the
spark igniter or igniter sensor. Prepare a short
jumper lead, using heavily insulated wire such as
ignition cable.
WARNING
High Voltage.
Can cause personal injury or death.
To prevent electric shock, do not allow fingers to
touch either the stripped end of the jumper or the
stud terminal.
3. Perform this test immediately upon energizing the
system, before the S8701 or S8702 goes into
lockout and interrupts the spark circuit. Touch one
end jumper firmly to the S8701/S8702 GND
terminal. Do not remove the existing ground lead.
Slowly move the other end of the jumper wire toward
the spark terminal on the control to establish a
spark. Pull the wire away from the spark terminal
and note the length of the gap at which spark
discontinues.
4. A spark length of 1/8 inch (3 mm) or more indicates
satisfactory voltage output. If no arc can be estab-
lished or the maximum spark is less than 1/8 inch
(3 mm), and power to the S8701 or S8702 input
terminals was proved, replace the S8701/S8702.
Ignition Cable
Check the electrical continuity of the ignition cable and
make certain the cable is not in contact with metal
surfaces. The total cable length should not exceed 6 ft
(1.8 m). Check connection to the spark terminal on the
S8701/S8702 and the boot connection to the igniter/
sensor. Make certain they are clean and tight.
Grounding Connections
A common ground is required for the burner, spark igniter
or igniter sensor mounting bracket, the 24 Vac (GND)
terminal and the GND (burner) terminal of the S8701/
S8702. If ground is poor or erratic, safety shutdown may
occur occasionally even though operation is normal at time
of checkout. Therefore, if nuisance shutdowns have been
reported, be sure to check ground connections.
Electrical ground connections at the spark igniter or igniter
sensor and the S8701/S8702 must be clean and tight. If
leadwire is damaged or deteriorated, use only a no. 14 to
18 gauge, moisture resistant, thermoplastic insulated wire
with the 105
°
C (221
°
F) minimum rating as a replacement.
Flame Sensor Circuit
The S8701 and S8702 provide ac power to the flame
sensor which the burner flame rectifies to direct current. If
the flame signal is less than 1.0
µ
A dc, the system will
lockout.
Check the flame sensing current from the sensor to the
S8701/S8702 control as follows:
1. Connect a meter (dc microammeter scale) in series
with the flame signal wire as shown in figures 4 and
5. Use the Honeywell W136A test meter or equiva-
lent. Disconnect the flame sense wire from the
sense terminal on the control. Connect the red
(positive) meter lead to the flame sense terminal on
the control. Connect the black (negative) meter lead
to the flame sense wire that goes to the flame rod.
2. Restart the system and read the meter. The flame
sensor current must be at least 1.0
µ
A and steady.
If the reading is less than 1.0
µ
A or unsteady , see
LOW OR UNSTEADY FLAME CURRENT section,
below. If flame is present at sensor and a reading of
0
µ
A is obtained, check for a secondary ground
connection to the 24 V (GND) terminal.
Fig. 6. S8701 Flame Current Measurement.
ALARM
VALVE
(GND)
SPARK
SENSE
RED (+)
BLACK (–)
MULTIPURPOSE
METER
1.2 µ A dc MINIMUM (AND STEADY)
M16236A
FLAME
SENSOR
BURNER
Fig. 7. S8702 Flame Current Measurement.
(See also S8701 Fig. 4).
GND
SENSE 2
VALVE (GND)
BURNER
(GND)
24 Vac (GND)
24 Vac
RED (+)
BLACK (–)
MULTIPURPOSE METER
1.2 µ A dc MINIMUM
(AND STEADY)
M16268A
FLAME
SENSOR
BURNER