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SERVICE PROCEDURE AG-III
Honeywell Thermowell Testing and
Replacemet
Step 1. If gas control has gone into lockout due to excessive tank temperature (four flashes and a three second
pause) reset the gas control to the “OFF” position. Then follow the instructions located on the lighting
instruction label or the lighting instructions located in the installation and operation manual.
Step 2. Observe the water heater operation. If the gas control continues to lockout due to excessive tank
temperature proceed to Step 3, thermowell testing, to determine the cause.
Step 3. To perform thermowell testing turn the gas control to the “OFF” position and disconnect the
thermowell harness from the gas control.
Step 4. Using a multimeter set to measure Ohms determine the resistance of the thermowell sensor (See
caution on this page).
Step 5. Hold one probe in the center pin and measure the outside positions pins (see figure 29 & 30).
Step 6. Refer to Table 1 on page 17 to determine the correct resistance value for the water heater tank
temperature.
Step 7. If the resistance values are correct the gas control needs to be replaced. If they are incorrect the
thermowell needs to be replaced.
Figure 28
Figure 29
Figure 30
CAUTION
DO NOT Use standard multimeter probes to
test. Doing so will damage connector. Use
special pin type electronic probes or small
diameter wire pins inserted into connector
Disconnect
thermowell wire
harness
Page 16
HONEYWELL THERMOWELL TESTING
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