69-1174
5
S8701/S8702 DIRECT SPARK IGNITION CONTROLS
NOTE:
If the gas control has been replaced or serviced,
lightoff may not be satisfactory until air has been
purged from the gas line or the gas input and
combustion air have been adjusted (see
manufacturer’s instructions).
Table 6. Trial for Ignition Periods for the S8701/S8702.
Check Trial for Ignition
1. Check device label on control to determine correct
Trial for Ignition time.
2. With the system power off and the thermostat or
temperature control set to call for heat, manually
shut off the gas supply.
3. Turn power on to energize the S8701/S8702,
immediately start timing when the gas valve turns
on.
4. Determine the number of seconds to drop-out of the
gas valve. It should not exceed the trial for ignition
time shown in Table 6.
5. After spark cutoff, manually reopen gas supply cock.
No gas should flow to the main burner.
6. Reset system as described below.
Resetting S8701 and S8702 After Safety
Lockout
If the control goes into safety lockout, it will remain locked
out for D and K models, until the system is reset.
To reset the system:
Adjust the temperature control setting to below room
temperature, wait 5 seconds, and move the temperature
control setting up to request heat or remove 24V power
and reapply. Normal ignition should occur as described in
Start System section.
NOTE:
F and M models have the 3 retry feature for Trial
for Ignition with 30 second interpurge between
TFI periods. Safety lockout on the F and M
models occurs after the 3rd TFI period if flame is
not sensed. F and M models also automatically
reset after one (1) hour in lockout.
CHECKOUT
Start the system and observe operation through at least
one complete cycle to make certain all controls are
operating safely.
Sequence of Operation
The S8701/S8702 controls perform the following basic
functions:
•
Supplies power to the electronic pulse-generator
circuit for the spark igniter (14,000 volts, open circuit).
•
Allows up to 23.75 seconds (maximum) for ignition
and 1 or 3 trials before system safety lockout occurs
(see Table 4).
•
Senses burner flame for safe lighting (2 burners for
S8702).
•
Shuts off spark after burner is lit.
The S8701 and S8702 are powered by a 24 Vac trans-
former and activated when the temperature control
requests heat.
Operation is as follows:
When the S8701/S8702 control is activated by the
temperature control’s request for heat, S8701/S8702
controls perform a safe-start check that determines proper
operation of the control before beginning the normal
sequence of operation. Once the Safe Start Check
operation passes, the control turns on the spark circuit and
at the same time, the S8701/S8702 opens the gas
control’s main valves, which allows gas to flow to the main
burner.
Power is supplied to the generator until:
•
The main burner(s) lights and the flame sensor
current reaches 1.0
µ
A, or
•
The ignition activation period ends
If the main burner lights, a flame sensing circuit is com-
pleted through the flame to the burner head to ground.
This current flow sets the Trial for Ignition timer to the reset
(normal) condition and interrupts the spark ignition circuit
(flame sense must occur on both burners on a S8702).
Should the current flow be interrupted, i.e., flame out
condition, the trial for ignition period begins again.
The S8701/S8702 will keep the gas control main valve
open as long as there is a request for heat and flame
current through the flame sensing circuit. If, however, the
trial for ignition timing period ends before the main burner
lights or the flame sensor establishes enough current, the
system will go into safety lockout or interpurge if the
control is an F or M model.
When the system goes into safety lockout, power to the
spark generator is interrupted, the power to the gas valve
is interrupted and the alarm circuit is completed and the
LED is steady on. The system will stay locked out until it is
reset by moving the temperature control setpoint to below
room temperature, no request for heat, for 5 seconds.
Then, re-energize the system by moving the temperature
control setpoint 5
°
F (3
°
C) above room temperature. Or,
remove 24 Vac power to the control then reapply.
NOTE:
F and M models will automatically reset from
lockout after one (1) hour.
Model
Specified Trial for
Ignition (TFI) (stamped
on control)
Trial for
Ignition Should
Not Exceed
S8701;
S8702
4.6 sec
6.6 sec
11.6 sec
21.6 sec
5.05 sec
7.25 sec
12.75 sec
23.75 sec
