On Tue, 11 Dec 2018 17:05:48 -0000, Colonel Edmund J. Burke wrote:

On 12/8/2018 10:02 AM, Clive Arthur wrote:
On 08/12/2018 17:51, Bruce Farquhar wrote:
On Sat, 08 Dec 2018 17:40:57 -0000, wrote:

On 12/8/18 11:41 AM, 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?

To *hold* the valve open only requires a small voltage & current. To
*pull* the valve open would require a larger voltage. That's why you
have to "Press & Hold" the manual knob to restart a pilot.

See here for more detail:
https://en.wikipedia.org/wiki/Thermo...pliance_safety

I see, thanks. I thought the "press and hold" was just to keep the valve open until the thermocouple warmed up. So I'm providing the effort to open the valve with my thumb. That link states 0.2-0.25A - do you really get that much current off a thermocouple?

Yes, it's a very low impedance source, a metal to different metal contact. 10mV 200mA is 50 milliohms. It's only 2mW, but that's a very small proportion of the pilot flame power.

Cheers

Don't forget to pigtail the neutral and ground circuits!

Assuming you mean these:
https://uk.rs-online.com/web/p/products/7643398
We use those in cars for the speaker circuits. Surely nobody uses anything that flimsy for power?

In the UK for power we use connector strips with grubscrews, like this:
www.ebay.co.uk/itm/192478665148