System Checks; Draft Test; Connections Check; Gas Pressure Checks - A.O. Smith GCV300 Service Handbook

SYSTEM CHECKS

Explosion Risk
WARNING! Before performing any
test, check the area around the water
heater for any source of a flammable
vapor (i.e gasoline, paint thinners,
etc.). If any sources are found, do not
proceed until they are removed.
Dra Test
WARNING! Burn Hazard. Do not
touch the vent. Doing so can cause
burns.
After successfully lighting the water
heater, allow the main burner to
operate for five minutes.
windows and doors and turn on all
gas appliances and air-moving devices
(range hoods, bathroom exhaust fans,
ceiling fans, etc.) in the home. Also,
close any fi replace dampers.
After five minutes, pass a newly
ex nguished match about one inch (1")
from the dra hood's relief opening.
Smoke from the match should be steadily
drawn into the opening, indica ng proper
dra and a func oning vent system.
DRAFT HOOD
MATCH
Figure 8.
If the main burner has been opera ng
for fi ve minutes, but the match smoke
dri s around or is blown away from
the opening, turn the gas control knob
OFF. Do not operate the water heater
until proper adjustments or repairs are
made to the vent pipe system and/or air
supply (p. 21). Always check the filter
and flame arrestor first and clean them,
if necessary (p. 18).
Connec ons Check
Some issues can be caused by faulty
connections. Refer to the following list
of connections when troubleshooting
the system:
• Igniter wire (Figure 9). See also
"Testing the Igniter System" on
page 19.
• Thermopile/thermal switch wires
at the gas control valve/thermostat
(Figure 9).
• Wire connections at the thermal
switch (TCO).
thermal switch wire can cause the
pilot to become inoperable. See
Figure 4, page 8.
See also "Diagnostic Flash Codes" on
Close all
page 10.
From Thermopile (White)
From Thermal Switch (Red)
RELIEF
OPENING
Igniter Wire
Manifold Flex Tube Nut:

Gas Pressure Checks

Gas pressure checks are made with
flowing gas. Use a gas pressure gauge
capable of reading pressure in inches
of water column.
A disconnected
Manifold
Pressure Tap
(1/8" NPT-RH)
Figure 9.
Residential Standard Gas Water Heater Service Handbook • 11
• Supply gas pressure checks are
measured before the gas control
valve/thermostat and as close
to the water heater as possible.
NOTE: The dynamic gas pressure
(burner on) should be measured
with all appliances operating that
use the common gas supply.
• Manifold (main burner)
pressure is measured at the
pressure tap on the bottom of
the gas control valve/thermostat.
See Figure 9 and Figure 11. Use a
3/16" Allen wrench to remove the
pressure tap plug, then attach the
gas gauge.
NOTE: Gas outlet pressures will be listed
on the gas control valve/thermostat's
pressure label. See Figure 10. Also,
gas supply pressure requirements are
shown on the water heater labeling.
GAS PRESSURE LABEL (OUTLET PRESSURE)
PRESSURE
CONNECTED AT
VAC
PRESSURE TAP
MANIFOLD GAS PRESSURE TEST
Figure 10.
CONNECTED AT PRESSURE TAP
Figure 11.
gas
GAS
GAUGE