As with the thermocouple, the open circuit test will tell us the potential output of the thermopile. While most thermopiles are designed to produce up to 750 mVDC, a minimum reading of 325 mVDC open circuit is generally acceptable as long as the switch is located close to the appliance and connected with properly sized wire. The one exception to this is the Comfort Control System which will require at Least 500 mVDC from each thermopile.

The test is carried out by removing the thermopile leads from the TP/TH and TP terminals and then placing your meter leads on the two wire terminals. Once again, your reading may be negative or positive depending on polarity, but it does not matter as we are concerned with the actual number.

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The closed circuit test will tell you the voltage drop across the main operator coil. With the switch or thermostat closed, place your meter leads on the TH and TP terminals and measure your drop in mVDC.