SAFETY CONTROLS, (cont'd.)
The Ignition Module is microprocessor based and operates on 24 VAC supplied by the transformer. The
control utilizes a microprocessor to continually and safely monitor, analyze, and control the proper operation
of the gas burners. The module with the presence of the flame sensor/ignitor or remote sensor, using flame
rectification, allows the heater to operate.
A "High Limit", is a safety device that opens the electrical circuit and shuts off the heater based on a
temperature set point within the "High Limit Device". The MiniMax NT Low NOx series of heaters
contains three (3) high limit devices, two (2) are located on the main inlet / outlet header, one sensing the
inlet water temperature and one sensing the outlet water temperature. The third high limit is located on the
exhaust outlet and senses the temperature of the flue gas.
OPERATION OF IGNITION MODULE
• When a call for heat is received from the thermostat supplying 24 VAC to the "W" module terminal, the
control will perform a self check routine, flash the diagnostic LED, on units manufactured prior to
10-15-01, (located on the module) for up to four seconds and begins the safety timing ignition sequence.
After the fan prepurge cycle, the hot surface ignitor is activated for a heat-up period followed by
energization of the gas valve for the trial for ignition period.
• When flame is detected during the trial for ignition, the ignitor is deactivated and the gas valve remains
energized. The thermostat and main burner flame are constantly monitored to assure the system
continues to operate properly. When the thermostat is satisfied and the demand for heat ends, the main
valve is de-energized immediately.
FAILURE TO LIGHT-LOCK OUT
Should the main burner fail to light, or flame is not detected during the trial for ignition period, the control
will go into lockout and the gas valve will be turned off immediately. The thermostat controller will display
a flame failure error (icon/service LED) and recovery from lockout requires a manual reset by either
resetting the 7800 Thermostat or removing 24 VAC from the system by turning off main power switch
(located on the junction box behind right door) for a period of 5 seconds.
If the established flame signal is lost while the burner is operating, the control will respond within 1 second.
The gas valve is de-energized and the control starts a new ignition sequence in an attempt to relight the
burner. If the burner does not relight, the control will go into lockout, requiring a manual reset.
Rev. C 11-1-01