MODU-FIRE® Forced Draft Gas-Fired Boiler
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3.7.3 Boiler Water Piping by Installer
3.7.3.1 Strainer
To avoid possible contamination of the boiler with dirt, rust or sediment from the system, a strainer near the boiler
inlet is strongly recommended. Even new systems may contain sufficient foreign material to eventually reduce the
performance of the heat exchanger. Adequate circulation of good clean water is essential to maximum efficiency
and long life of the boiler.
3.7.3.2 Relief Valve and Piping
Each boiler is supplied with a pressure-relief valve sized in accordance with ASME requirements. The relief valve
must be piped to a suitable drain prior to placing the boiler into service and in a manner that prevents water spray
from contacting any person. Reducing couplings or other restrictions are not permitted in the discharge line.
Do not plug or obstruct the discharge of the relief valve.
3.7.3.3 Low Water Cut-off
The boiler is furnished with a flow-switch-type low water cut-off as required by the ASME BPV Code, Section IV;
no field piping is required. If the flow switch does not sense water flow, the boiler will shut down and a red indica-
tor will be illuminated on the control panel.
Installation of an external low water cutoff or manual reset low-water switch may be required by certain codes or in
certain installations. Consult your local code for details.
Never install a valve that can isolate the low water cut-off from the boiler.
3.7.3.4 Drain Valve and Piping
The boiler is not provided with external drain connections. A drain valve should be installed near the inlet (system
return) connection to the boiler and piped to a suitable floor drain. The boiler can be completely drained through
the bottom header by removing the flush plug in the bottom end plate.
This plug may also be used to flush accumulated sediment from the bottom of the boiler.
3.7.4 Flushing and Filling
3.7.4.1 Flushing the System
Before filling the boiler, flush the system to remove the debris. Clean and flush old piping thoroughly before
installing the boiler as recommended by your water conditioning or chemical treatment supplier.
Under no circumstances should the hydronic system be flushed while the boiler is attached to the system since
the debris or corrosion products could accumulate in the boiler and plug the boiler heat exchanger.
If the piping system attached to this unit will be chemically cleaned, the boiler must be disconnected from the
system and a bypass installed so that the chemical cleaning solution does not circulate through the boiler.
3.7.4.2 Filling
To be sure that the boiler is not air-bound, open the pressure-relief valve located at the rear of the boiler. Leave
the relief valve open until a steady flow of water is observed. Close the valve and finish filling the system.