In a so called milliVolt heating system, BOTH the pilot valve and the main gas valve are controlled by low voltage valves.

You need to press and hold the button to light the pilot to give the thermopile a chance to heat up so it can continue to hold the pilot valve open.

The main valve is controlled by the Tstat using the small voltage generated by the thermopile.

I don't know about newer systems with flue dampers etc but the older mVolt systems worked without any grid power at all, all the electricity was generated by the thermopile heated by the pilot light.


mark




The thermopile voltage is very low but the current is high enough to operate the valves that are designed to work on very low voltage.