A.O. Smith HW 300 Instruction Manual page 27

2. PILOT BURNER - ELECTRONIC IGNITION
To establish pilot flame without main burner operation, it will be
necessary to perform the following steps:
Servicing of the pilot burner (every six months) includes
keeping pilot shield (not shown) free of lint, cleaning the burner
head, the primary air opening and the orifice of the pilot burner,
Figure 20.
a. Open fused disconnect switch or shut off electrical power to
the boiler.
b. Disconnect wire from MV wire on valve.
c. Close fused disconnect switch to restore electrical power to
the boiler.
The pilot will now ignite provided the system is calling for heat.
d. Adjust pilot flame.
To adjust the pilot flame, remove the cap screw from the pilot
adjusting screw (Figure 21) and turn to deliver a sufficient flame
at the pilot burner to cover 3/8" to 1/2" (10-12 mm) of the sensing
probe tip. See Figure 20.
Check for good terminal connection at the sensing probe at the
pilot burner assembly if pilot does not light.
FIGURE 20. SPARK IGNITION PILOT BURNER AND BURNER FLAME
FIGURE 21. ADJUSTING PILOT FLAME
Check for electrical power to the valve. If electrical power and
gas are present at the valve and the pilot does not operate when
system calls for heat, replace valve.
e. Low gas pressure
• Adjust pilot flame by means of the pilot gas adjustment
located in the gas control valve.
• The pilot flame should envelop 3/8 to 1/2 inch (10-
12 mm) of the tip of the thermocouple. Remove pilot
adjustment cover screw, Figure 21. Turn inner adjustment
screw or pilot adjusting valve clockwise to decrease,
or counterclockwise to increase pilot flame. Be sure to
replace cover screw on combination gas control valve
after adjustment to prevent possible gas leakage.
f. Clogged pilot burner orifice.
• Clean or replace orifice. A clogged orifice will restrict gas
flow and result in low thermocouple output.
g. Incorrect orifice.
• Replace. The Orifice size is stamped on the wrench flats.
h. Clogged primary air opening.
• Restricted air passages will soften the pilot flame and
result in poor thermocouple flame impingement.
27