On Sun, 09 Dec 2018 08:19:13 -0000, gregz wrote:

"Bruce Farquhar" wrote:
On older boilers (furnaces if you're American), when the heating isn't
actually running (eg. the thermostat says the house is warm enough),
there's no power to the boiler, so how does the pilot light valve stay
open with the tiny voltage (40mV?) and current from the thermocouple?

What are they using, real boiler steam heat, or hot water ?

In the UK we use hot water, about 70 to 80C. This heats (by a heat exchanger) the hot water tank, and directly the radiators full of water. Or more modern ones heat the water for hot taps directly, but those are new enough to not use pilot lights, they have electric spark ignition.