On Sat, 08 Dec 2018 18:32:08 -0000, Max Demian wrote:

On 08/12/2018 16:41, 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?

Well they used to have a bimetallic strip to hold the pilot light valve
open rather than a thermocouple. Or maybe that's when boilers didn't
have an electrical connection at all.

The electricity from the mains supply (on an old basic/system boiler/furnace) is nothing to do with the pilot light, it just operates the main gas valve. The mains connection to my boiler is only on when the room stat calls for heat. When the room is warm enough, no electricity is given to the boiler at all.

What do you mean "when boilers didn't have an electrical connection at all"? Surely they need something to tell them to start burning gas?