Bock Water heaters OT300-A Installation And Operation Instruction Manual page 39

SECTION VI: MAINTENANCE (cont.)
FLUSH THE TANK
Elements in the water such as lime and iron may accumulate in the heater. Accumulation of
these elements can keep your water heater from operating at peak efficiency and may lead to
premature tank failure. It is recommended that the tank is drained and flushed thoroughly
twice a year to prevent buildup.
CHECK THE COMBUSTION SYSTEM
On an annual basis, verify that the combustion system is operating within acceptable
parameters. Gas pressures and combustion measurements can be used to verify proper
operation.
• Check the inlet gas pressure to the gas control. The pressure should be greater than 6" W.C.
when the burner is operating at high fire. Gas pressure shall not exceed 14" W.C. when the
burner is off.
• Measure the products of combustion in the exhaust vent. At maximum input, the % O2 in
the exhaust gas should be in the range of 3.0 - 4.5%. CO should be less than 25 ppm.
• If the combustion readings are outside of the specified ranges, check the manifold pressure
on the gas control at the outlet pressure tap. See Figure 30 for the location of this pressure
tap on the gas control. At maximum input and minimum vent lengths with 4" pipe, the
manifold pressures for each model are approximately:
• Models OT300N, OT300N-A: -1.0" W.C.
• Models OT400N, OT400N-A: -1.6" W.C.
• Models OT500N, OT500N-A: -2.4" W.C.
Contact Bock Water Heaters if the measured manifold pressure varies by +/- 0.5" W.C. or
greater from the specified value.
Figure 30: Honeywell Gas Control (Top View)
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