One more questoin about gas boilers.

For the outcome of my friend's boiler problem, see the next post.
One more questoin about gas boilers. Why on this commercial or semi-commeicial boiler are there two control circuits of different voltages? And since the 24volt circuit controls the mian electric gas valve and thus turns the burners on and off, , what does the 110 volt circuit control?
There is one circuit that has in it a 24 volt transformer output, the pilot swich, which turns off the pilot and interrupts the electric circuit if the pilot goes outt, the therrmostat which interrupts the the same electric circuit and turns off the main electric gas valve (but not the pilot, and that mail electric gas valve, which opens when the thermostat calls for heat (and the pilot is lit.)
There was also the Low-water cutout, which controls 110 volts AC. I read that it is in the same circuit as the High Presssure cutout, the maybe a low pressure cutout and other safety devices.
But how doe sthis turn off the gas when there's a problem. What does it contrrol? How come these 3 sefety devices aren't just in series with the thermostat and the pilot switch?. I know they're not because that circuit is 110volts and this one is 24 volts??
Does the main electric gas controlv valve turn off from both the absences of 24 volts and the absence of 110 volts? How come these 3 sefety devices aren't just in series with the thermostat and the pilot switch?
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wrote:

Simple question - is the 24 volt transformer primary(120volt) controlled by the 120 volt control?? If so, the 120 volt shut-off will also shut off anything controlled by the 24 volt system.
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On Sat, 22 Dec 2012 17:02:18 -0500, snipped-for-privacy@snyder.on.ca wrote:

Maybe I'm as stupid as my friend, for not thinking of that. I don't know, because I didn't do enough measurements (one more would have done it) and the route of the wires was't visible, , but that would certainly account for everything, and very simply. I'll figure that's it. Thanks.
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120 volt control might run the circulator pump. Have to be there, and trace a few wires to know for sure.
Christopher A. Young Learn more about Jesus www.lds.org .

Maybe I'm as stupid as my friend, for not thinking of that. I don't know, because I didn't do enough measurements (one more would have done it) and the route of the wires was't visible, , but that would certainly account for everything, and very simply. I'll figure that's it. Thanks.
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On 12/22/2012 3:36 PM, micky wrote:

Wouldn't the 110 VAC circuit also be supplying the 24 VAC transformer?
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Because you typically have one circuit where it's desirable to have low voltage, eg the thermostat wiring, gas valve, zone valves, etc. IT would be a real pain to have to run 120V to all those, plus 24V can't kill anyone. Nor is 120V required, because the power reqts of those devices is low.
And you have other circuits, eg circulator pump, that needs the power that 120V circuit can supply.
>And since the 24volt circuit controls the mian electric gas

Run the circulator pump? Inducer fan if it's a high efficiency boiler?

Isn't the 24V transformer part of the boiler and powered by the 120V AC circuit? That may answer your questions.
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On Sun, 23 Dec 2012 06:46:10 -0800 (PST), " snipped-for-privacy@optonline.net"
;;;;;;

Yes, it does. Thank you Trader and George.
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