MODU-FIRE® Forced Draft Gas-Fired Boiler
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drive to the position to provide heat to the DHW loop. This output provides 120VAC 0.5Amp service to HV14.
The neutral for this circuit is provided on HV 6.
DHW Pump Relay w/Delay Off - This output is enabled when there is a call for DHW. When the call for heat is
removed, the output remains enabled for a predetermined period of time. The time delay is adjustable through the
ENVI™ control system. This output provides 120VAC 0.5Amp service to HV15. The neutral for this circuit is
provided on HV 7.
Circ Pump Relay w/Delay Off - This output is enabled when there is a call for heat. When the call for heat is
removed, the output remains enabled for a predetermined period of time. The time delay is adjustable through the
ENVI™ control system. This output provides 120VAC 0.5Amp service to HV16. The neutral for this circuit is
provided on HV 8.
Damper Relay - This output is enabled when the call for heat is enabled. This output provides 120VAC service
to HV17. The neutral for this circuit is provided on HV 9. This circuit is for pilot duty only (less than 1 amp).
Master Alarm Relay – This contact closes in the event of an alarm output from the boiler control, connecting
HV18 and HV19.
Flame Detected Relay – This contact closes whenever the boiler is firing, connecting HV20 and HV21.
3.4.2 Low Voltage (LV) Terminal Block
Enable/Disable– Use for boiler enable. Closing this circuit allows the boiler to run. Opening this circuit prevents
the boiler from running, provided the remote/local enable switch is in the remote position. This circuit is energized
by the boiler. It has a 24VAC potential. Devices connected to these terminals must be rated for 24VAC.
The remote/local enable switch bypasses the Enable/Disable (LV1 to LV2)
when in the local position. Do not connect safety devices into the Enable/Disable circuit.
Auxiliary Low Water Cutoff – These terminals are used for connection of a secondary low water cutoff used in
the system. This circuit is energized by the boiler. It has a 5V potential. Devices connected to these terminals
must be rated for 5V.
Start Interlock - Use for attachment of an additional field safety device to the boiler control circuit. Closing this
circuit allows the boiler to run. Opening this circuit prevents the boiler from running. This circuit is energized by
the boiler with a 5V potential. Devices connected to these terminals must be rated for 5V.
Outdoor Temp Sensor – LV7 and LV8 are connected to the outdoor temperature sensor. The temperature
control must be programmed to run an outdoor air schedule. The outdoor air sensor and programming help are
available from the ENVI™ Advanced User’s Guide (ENVI™ 09) or from your local Harsco Industrial, Patterson-
Kelley Representative. This circuit is energized by the boiler with a 5V potential. The temperature sensor must be
a NTC having 12k@25°C.
DHW Stat/Sensor – LV9 and LV10 are connected to the DHW temperature sensor or thermostat. This circuit is
energized by the boiler with a 5V potential. The temperature sensor must be a NTC having 12k@25°C.
Header Temp Sensor – LV11 and LV12 are connected to the header temperature sensor. This circuit is
energized by the boiler with a 5V potential. The temperature sensor must be a NTC having 12k@25°C.
