How does my boiler get power?

umscheidt

I recently bought a house with an older steam boiler. I’ve read we’ve got steam and the lost art of steam heating to understand my system and make it more efficient.

One thing I’m not clear on is how does my boiler power the electronics like the pilot for the burners and pressuretrol? I ask as I don’t see any 120v wires anywhere. 

The only two wires I see run to the thermostat and the gas shut off switch on the basement steps. 

Also I don’t see any emergency switch on the boiler. Should I have one? Or is that the same as the gas shut off found on the steps?

WMno57

Your boiler probably has a PowerPile gas valve.
https://www.supplyhouse.com/Resideo-VS820A1047-Standard-PowerPile-Millivolt-Combination-Gas-Valve-1-2-NPT-x-3-4-NPT
You will be warm and laughing at the rest of us when the grid dies from too many Heat Pumps.
If I had your boiler, I would never replace it. Unless it was leaking.

WMno57

"These gas controls combine a Lite-Rite manual gas cock, safety shutoff Pilotstat assembly, millivoltage automatic valve operator, and optional gas pressure regulator. They require the use of a 750 mv Powerpile generator (thermopile). The generator, heated by the pilot burner flame, provides the electrical energy to operate the combination gas control. A millivoltage thermostat with suitable accessory controls completes the automatic control system for the heating appliance."

quoted from
https://www.supplyhouse.com/Resideo-VS820A1047-Standard-PowerPile-Millivolt-Combination-Gas-Valve-1-2-NPT-x-3-4-NPT

EBEBRATT-Ed

The one thing I don't like about a millivolt system is the only way to shut it down is the thermostat

WMno57

Good post here from 2009 by @Tim McElwain .
https://forum.heatinghelp.com/discussion/comment/1175822/#Comment_1175822
He discusses the typical lifespan of the powerpile generator and how the gas valve is only single seat. Per Tim, gas code now requires gas valves to be double seat.

mattmia2

I think you have a transformer somewhere else in the thermostat wiring though it could be millivolt. Show us the label on the side of the gas valve. Most thermopiles have a cable with spade terminals instead of the coaxial connection you have.

EdTheHeaterMan

EBEBRATT-Ed said:

The one thing I don't like about a millivolt system is the only way to shut it down is the thermostat

I can see at least two other off switches in these photos, ED!

mattmia2 said:

I think you have a transformer somewhere else in the thermostat wiring though it could be millivolt. Show us the label on the side of the gas valve. Most thermopiles have a cable with spade terminals instead of the coaxial connection you have.

The Robertshaw 750MV valve model 700-502, 700-504, and 700-506 have coaxial thermopile connection.
https://s3.amazonaws.com/s3.supplyhouse.com/manuals/1255649090857/18032_PROD_FILE.pdf

and Weil McLain EG series 1 offered "Self Generating Control" as an option.

Intplm.

I sure do miss the thermocouple.

Chris_L

I don't think this is a millivolt system. Isn't that an aquastat to the left of the sight glass? Will that work on millivolts?

EdTheHeaterMan

Chris_L said:

I don't think this is a millivolt system. Isn't that an aquastat to the left of the sight glass? Will that work on millivolts?

YES, that will open and close regardless of the amount of electricity that is passing thru those contacts. the aquastat is there to maintain about 170° or so, for a tankless coil. It is the same wiring as a 24 volt control system Just without the 24 volts. it's 750 MV instead

If you look at the post above you can see that MV was an option from Weil McLain back in the day.

Chris_L

EdTheHeaterMan said:

Chris_L said:

I don't think this is a millivolt system. Isn't that an aquastat to the left of the sight glass? Will that work on millivolts?

YES, that will open and close regardless of the amount of electricity that is passing thru those contacts. the aquastat is there to maintain about 170° or so, for a tankless coil. It is the same wiring as a 24 volt control system Just without the 24 volts. it's 750 MV instead

If you look at the post above you can see that MV was an option from Weil McLain back in the day.

Yes, but that gas valve doesn't look like a 100% shutoff, millivolt valve. And where are the dual limits (P-trols). I see only one.

umscheidt

Very interesting thanks all!

EdTheHeaterMan

Chris_L said:

EdTheHeaterMan said:

Chris_L said:

I don't think this is a millivolt system. Isn't that an aquastat to the left of the sight glass? Will that work on millivolts?

YES, that will open and close regardless of the amount of electricity that is passing thru those contacts. the aquastat is there to maintain about 170° or so, for a tankless coil. It is the same wiring as a 24 volt control system Just without the 24 volts. it's 750 MV instead

If you look at the post above you can see that MV was an option from Weil McLain back in the day.

Yes, but that gas valve doesn't look like a 100% shutoff, millivolt valve. And where are the dual limits (P-trols). I see only one.

It may not look like it... But it IS. look at this old Robertshaw model 700 Cut Sheet. 750MV valve model 700-502, 700-504, and 700-506 have coaxial thermopile connection
And this is the Pilot Generator. https://www.supplyhouse.com/Robertshaw-1951-001-36-Thermopile-Generator-w-Coaxial-Connection-and-PG9-Pilot-Adaptor