P/N 472235 Rev. B 1-22-04
26
SAFETY CONTROLS, (cont’d.)
IGNITION MODULE
The Ignition Module is microprocessor based and operates on 24 VAC supplied by the transformer. The
module monitors the demand for heat, controls the combustion blower, monitors proper air flow, ignites and
maintains the flame during heating and provides diagnostic support. The on-board diagnostics, with LED
output, provides assistance with troubleshooting and ensures safe and efficient burner operation.
HIGH LIMITS
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/TSI Low NOx series of heaters
contains two (2) high limit devices, located on the main inlet / outlet header, one sensing the inlet water
temperature and one sensing the outlet water temperature.
OPERATION OF IGNITION MODULE
HEAT MODE
• When a call for heat is received from the thermostat supplying 24 VAC to the module terminal, the
control will perform a self check routine, then begins the ignition timing 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, through the flame sensor, 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 and post purge cycle will start and continue for
approximately 45 seconds where the combustion blower stops.
FAILURE TO LIGHT THE BURNER—LOCK OUT
Should the main burners fail to light, or flame is not detected during the trial for ignition period, the ignition
Module will stop the ignition sequence and the gas valve will be turned off. The ignition module will go
through this sequence three (3) times, if full ignition fails after the third try, the module will go to full lock
out. To restart the ignition sequence, turn the main electrical power off to the heater, using the switch on the
bottom of the junction box, for a period of one minute, then turn the power back on, the heater will again try
to light.
FLAME FAILURE—RE-IGNITION
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. The ignition attempt will be repeated (3) times. If the burner does not relight, the control will go into
lockout, requiring a manual reset.
Basic Operation
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