How do you know if the thermopile is bad?
The thermopile can be read with a multimeter to check if its the cause of the problem. Three hundred millivolts or higher voltage is a sign of a good thermopile. A reading below 300 millivolts would require you to replace the thermopile. If the thermopile does not generate the correct voltage, the thermocouples in the collection cannot generate enough current to power the control panel, the heater may fail to provide you hot water.