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Testing a Thermocouple’s Voltage

Step 1: Disconnect the thermocouple from the bottom of the gas control.
Disconnect thermocouple from gas control

Step 2: Set your voltmeter to millivolts (mV) and direct current (DC).
Set voltmeter for mV and DC

Step 3: Set gas controls for pilot lighting.
Turn gas controls for pilot lighting

Step 4: Attach the positive lead (Red) to the bare copper, and the common lead (Black) to the end of the thermocouple.
Attaching the leads to the thermocouple

Step 5: Light the pilot, and continue to hold the pilot switch down until maximum voltage is reached. Normal operation for most water heaters is 17-32 mV. If it falls below this range a replacement thermocouple may be needed.
Light the pilot