1) Call for Heat
- The thermostat calls for heat by energizing the “W” ter-
minal. The control checks to see that the limit switches are closed and the
pressure switch is open. If one of the limit switches is open, the control
responds as defined in the “Abnormal Heat Cycle, Limit Switch Operation”.
If the pressure switch is closed, the control will do four flashes on the green
LED and wait indefinitely for the pressure switch to open. If the pressure
switch is open, the control proceeds to prepurge.
2) Prepurge -
The control energizes the venter motor and waits for the
pressure switch to close. If the pressure switch does not close within 30
seconds of the venter motor energizing, the control will do two flashes on
the green LED. The control will leave the venter motor energized indefi
-
nitely as long as the call for heat remains and the pressure switch is open.
When the pressure switch is proven closed, the control begins the pre-
purge time. If flame is present any time while in prepurge, the prepurge
time is restarted. If flame is present long enough to cause lockout, the con
-
trol responds as defined in “Fault Modes, Undesired Flame”.
The control runs the venter motor for a 20 second prepurge time, then pro-
ceeds to the ignition trial period.
3) Ignition Trial Period -
The control energizes the spark and main gas
valve. The venter remains energized. If flame is sensed during the first
16 seconds, the spark is de-energized and the control proceeds to heat
fan/blower on delay. If flame has not been sensed during the first 16 sec
-
onds, the control de-energizes the spark output and keeps the gas valve
energized for an additional one second flame proving period. If flame is not
This heater is equipped with a direct spark integrated control module (circuit
board). The module monitors the safety devices and controls the operation
of the fan and venter motors and the gas valve between heat cycles.
10. Ignition System
Control Status - Green LED Codes
Steady ON .....Normal Operation, No call for heat
Fast Flash ......Normal Operation, Call for heat
1 Flash ...........System Lockout, Failed to detect or
sustain flame
2 Flashes .......Pressure Switch Did Not Close
within 30 Seconds of Venter motor
3 Flashes .......High Limit or Vent Temperature
Limit Switch Open
4 Flashes .......Pressure switch is closed before
venter motor is energized
Steady OFF ...Blown Fuse, No Power, or Defec-
tive Board
Flame Status - Yellow LED Codes
Steady ON .....Flame is sensed
Slow Flash .....
Weak flame (current below 1.0
microamps ±50%)
Fast Flash ......
Undesired Flame (valve open and
no call for heat)
FIGURE 11 – DSI
Integrated Control
Module (circuit board)
�����
�����������
�������
����
����
����������
�����������
����������
���
�����
������
������
�
LED Lights
Dip
Switch
LED lights are visible through a viewport.
Fan/Blower OFF Delay Settings
(dip switches)
S
W-1 SW-2 Time
Off
Off
120 seconds (factory setting)
Off
On
90 seconds
On
Off
160 seconds
On
On
45 seconds
Normal Heat
Cycle Operating
Sequence
Form I-UEAS, Page 34
