On Sat, 08 Dec 2018 20:33:27 -0000, Rod Speed wrote:



"Bruce Farquhar" wrote in message
news
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?

Doesn't have to be an electrical thermostat, can be
a bimetallic thermostat or a bulb and capillary tube.

For the internal stat for its own tank, yes. But the room stat needs to tell the boiler remotely, which is always electricity surely.