On Dec 11, 9:00*am, RBM wrote:
On 12/10/2011 10:34 PM, croy wrote: My new wall heater has a gas valve that is thermostatically
compatible. *The most common thermostat for this heater is
called a "microvolt" thermostat. *It apparently get its
microvolts from something heated by the pilot light.

What I can't seem to get my head around, is how can such a
small amount of power manage to horse-open the rather high
flow gas valve?

It uses a pilot generator to make electricity which powers the coil on
the valve. The down side is that it generally takes a while to operate,
unlike a 24 or 120 volt coil valve

Sounds like it's the same type of system used on most
water heaters that also don't have any external power
source to open the gas valve.