About furnace gas valves of the millivolt type, that typically work from a ~750 millivolt thermopile source.

What is the current to maintain the valve open in operation ? Is it a solenoid ? Maaany places mention only the millivolts, and cannot find the working current requierements for the valve.

 

The solenoid that holds the gas valve open has a resistance of only a fraction of an Ohm, so even 750mV can drive a current > 1A through it to create a strong magnetic field.