Thermopile Check (Open Circuit); Thermopile Check (Closed Circuit) - A.O. Smith GCV300 Service Handbook

Table 3.
Gas Pressures
IF . . .
. . . THEN
...the supply gas • increase the
pressure is lower supply gas
than required... pressure regulator
setting
and/or
• increase supply
gas piping size.
...the supply • add a gas pressure
gas pressure regulator.
is higher than
• reduce the setting
required...
on the existing
regulator.
...the manifold • ensure that there
gas pressure is adequate supply
is not within gas pressure
+/- 10% of the
• ensure that the
value shown
main burner
on the gas
orifice is the
pressure label...
correct size for
the model being
tested.
NOTE: The gas
pressure label • if the above
lists the gas
tests have been
valve outlet performed and
pressure. This
the results were
is the same as correct, replace
the manifold
the gas control
pressure. See valve (p. 20).
Figure 10.
Thermopile Check
(Open Circuit)
The following test will check the DC
voltage generated by the thermopile
when the pilot light is lit.
1. Remove the connectors from the
gas control valve/thermostat (red
and white wires). Use needle-nose
pliers.
12 • Residential Standard Gas Water Service Handbook
2. Insert multimeter leads into the
connectors. The multimeter must
be set to read millivolts DC (on a
scale that can read 750 millivolts).
Reference Figure 12.
USE A MULTIMETER TO CHECK THE OUTPUT OF
THE THERMOPILE (MEASURED IN MILLIVOLTS).
SHOWN ABOVE - MULTIMETER PROBES ARE
INSERTED INTO THE THERMOPILE PLUGS. THESE
PLUGS WERE REMOVED FROM THE RECEPTACLE AT
THE BOTTOM, RIGHT-HAND CORNER OF THE GAS
CONTROL VALVE/ THERMOSTAT.
Figure 12.
3. Follow the lighting instructions to
light the pilot. Once the pilot is lit,
continue to hold the gas control
knob in until this test is complete.
You may need assistance from
another person to do this. The
voltage reading should
gradually as the thermopile heats
up. After a few minutes, you should
have a reading of at least 350 mV
DC. A reading above 350 mV DC
indicates that the thermopile is
working properly.
4. When you are finished, plug the
connectors back into the gas
control valve/thermostat. If the
connectors are separate (not a
double connector), ensure that the
red wire connector is to the left and
the white wire connector is to the
right. See Figure 2B, page 7. If
the status light does not blink once
every three seconds, replace the
gas control valve/thermostat.
Thermopile Check
(Closed Circuit)
Follow the lighting instructions to light
the pilot. Once the pilot is lit, you can
check the output of the thermopile
with one of the following tests. A
reading above 350 mV DC indicates
that the thermopile is working
properly.
INSERT MULTIMETER LEADS INTO
THERMOPILE PLUGS AT CONTROL.
PILOT MUST BE LIT.
MULTIMETER SET TO READ mV.
MINIMUM ACCEPTABLE
MEASUREMENT: 350 mV DC.
Figure 13.
INSERT ONE MULTIMETER LEAD INTO
THE NEGATIVE PLUG ON THE CONTROL
(WHITE WIRE).
rise
TOUCH THE OTHER LEAD TO A
TERMINAL ON THE THERMAL
SWITCH (TCO).
MULTIMETER SET TO READ mV.
PILOT MUST BE LIT.
MINIMUM ACCEPTABLE
MEASUREMENT: 350 mV DC.
Figure 14.