Page 16 / IM 685
Service
General
Before starting service on this burner take the time to read the sections "About This Burner" and the
"Sequence of Operation" to get an overview.
Gun Assembly
The McQuay gas burner gun assembly is easily removable and includes the ignition electrode assembly,
the flame rod assembly, and a "Base Air" fitting with orifice. The positioning of this assembly is not
considered field adjustable. When positioned correctly the gun disc will be perpendicular to the blast
tube and back in the cylindrical portion of the blast tube as shown in Figure 8. The gun pipe will be
concentric with the blast tube.
Figure 8. Gun Assembly
Gun Assembly Removal and Installation
Unplug the ignition lead from the ignition electrode and unplug the flame rod lead from the flame rod.
Disconnect the
3
⁄
8
inch copper tube at the brass fitting on the left side of the gun pipe, open the pipe
union and remove the gun assembly. Models 050-200 include an air tube that must be lifted up and out
of the grommeted hole it is nested into as the gun assembly is removed. The gun assembly may have to
be manipulated and wiggled as the disc is withdrawn back through the blast tube. Reassemble in reverse
order, being particularly careful to correctly reinsert the air tube into the grommeted hole. The tube
should slip into the grommet so there is little leakage, but it should not bear down on it or it can cause
binding on the sliding air valve. Always remove shoulder screw (12), Figure 16a, and manually slide the
control rod back and forth to test for binding after reinstalling the gun assembly on Models HT050-
200. Do not operate the burner without a tight seal at the grommet.
Flame Rod Adjustment
The gun assembly is removed for flame rod inspection or service. When correctly adjusted the flame rod
insulator will be concentric with the hole it passes through, not be shorted out against the disc, the 0.75
inch long end tip will point toward the 0.086 inch diameter alignment hole, and the end tip will clear
the disc according to dimension ‘C’ Figure 9.
Figure 9. Flame Rod and Ignition Electrode
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