MODU-FIRE® Forced Draft Gas-Fired Boiler
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temperature control (see Section 3.11 for instructions on setting this control). After completion of these tests, re-
adjust the operating thermostat to the desired operating temperature and set high-limit temperature, typically 20º
F above operating temperature.
3.10.4 Test of Low Gas Pressure Switch
Hi/Low Gas Pressure Switch
The boiler is furnished with a low gas pressure switch. The operation of this switch must be checked by slowly
closing the main gas cock while the burner is operating. The switch should shut down the main burner. The
control will display LOW GAS PRESSURE. This is a manual reset error and the boiler should not start until the
gas valve is opened, the low gas pressure switch is reset, and the control is reset.
3.10.5 Test of High Gas Pressure Switch
The boiler is furnished with a high gas pressure switch. The operation of this switch must be checked by closing
the downstream main gas cock, and starting the boiler. Once the trial for ignition period is reached, the main gas
valve will open, pressurizing the line. This will trip the high gas pressure switch. The switch should shut down the
main burner. The control will display HIGH GAS PRESSURE. This is a manual reset error and the boiler should
not start until the gas valve is opened, the low gas pressure switch is reset, and the control is reset.
3.11 Boiler Operating Control
The MODU-FIRE® Forced Draft boiler is equipped with a combination combustion and temperature control. This
control monitors combustion and lighting of the boiler, as well as maintaining temperature of the supply water.
The temperature control portion modulates the boiler to maintain the desired outlet temperature based on the
selected operating configuration.
3.11.1 Initial Adjustments
The MODU-FIRE
®
Forced Draft 750-2000 boilers are
equipped with ENVI™ control; an intelligent control
system with advanced features such as text-based
display, communication capabilities, and boiler
sequencing. Errors are date and time stamped
providing built-in history of boiler status and
performance. This control constantly tracks the load
by recording burner high, low and mid run hours. One
control to do it all – temperature control, flame
safeguard, firing rate control, blocked flue protection,
outdoor air reset, freeze protection, built-in cascade
sequencing, MODBUS® communication and more.
Manual Reset
