What voltage range indicates a healthy safety valve using a thermocouple?

The voltage range of 12 to 15 millivolts (mv) is indicative of a healthy safety valve when using a thermocouple to measure the millivolt output. This voltage level suggests that the thermocouple is effectively generating an adequate millivolt signal, which is essential for the proper functioning of the safety system.

In a gas appliance, the thermocouple works by converting heat from the pilot flame into a small voltage. This voltage is what keeps the safety valve open, allowing gas to flow when the pilot light is lit. If the thermocouple produces a voltage within the 12 to 15 mv range, it indicates that the thermocouple is functioning optimally, providing sufficient voltage to maintain the safety valve's operation.

By contrast, lower or higher voltage readings may suggest issues such as a weak thermocouple or poor flame contact, which would not ensure safe operation. Understanding this range is crucial for technicians when diagnosing and ensuring that gas appliances operate safely and efficiently.