Can my vintage boiler wiring be updated to modern wiring?

Any competent licensed electrician can replace that older wiring with modern wiring and connect to your existing boiler controls, while feeding power from a new independent circuit.

That thing is running really lean.

what is the second pole of the switch used for(i remember trying to figure that out in another thread)? are those 24vac transformers? the fused switch itself can be replaced with a modern toggle switch. if the transformers are 24vac I would replace them with a new transformer because the primary wiring is likely to crumble as soon as you start trying to bend it.

like others said you would wire a new dedicated circuit to it because central heating equipment has to be on its own circuit.

is one of those xfmrs for a doorbell?

As I see your setup, you have old cloth-insulated wiring for both the line voltage and the low-voltage wiring. There was nothing wrong with that when it was installed, and you can also use 14-gauge wiring for the new control wiring to keep the look original. Any electrician will certainly want to remove and replace all the wiring

The fuse box can be replaced with a standard 15-amp switch in a standard junction box. The 15-amp breaker in your new circuit breaker panel is all you need for the dedicated circuit.

The only 120 VAC item in your setup is the transformer. It does not even draw 5 amps, so the 15-amp breaker and 14-gauge wires from the panel are sufficient.

Where I think you should change the control strategy is with the 24 VAC transformer. I would replace it with a new one for the reason @mattmia2 mentioned: the wire insulation will likely crumble as soon as you start working with it, and a replacement transformer is not that expensive.

The next step is to connect all the controls with thermostat wire in series from the transformer R terminal to the thermostat, (red wires) then to the limit(s), and then to the gas valve. From the gas valve, you need a return path back to the transformer C terminal (blue wire).

Other limits could be a spill switch at the draft diverter to open the electric circuit to the gas valve if the chimney ever gets blocked. The burner shuts because the hot exhaust gasses can't exit the building.  You certainly don't want to be breathing that stuff all night and wake up dead the next day.

That gas valve is not original to the boiler or burner system you have. It is a modern redundant gas valve and has more safety features than the original gas valve and pressure regulators with the pilot safety switch on the wall around the corner from the transformer. So keep that gas valve you have, unless you want to upgrade to electronic ignition. 

Depending on the size of the pilot that may save you a little on your annual gas bill but only about $20.00 to $40.00 per year if it has a large flame pilot burner this is the kit for that Electronic Ignition retrofit kit

Your electrician may not want to get involved with the old boiler to install that kit so think about before you buy.  You will need a gas heat guy that isn’t afraid of old stuff. 

@EBEBRATT-Ed has a concern about your statement about the Honeywell high limit control being disconnected.  Do you know for sure that the control no longer shuts off the burner?  If that is true, then you need to add some kind of high limit control to protect the boiler from overheating and causing a catastrophic failure.  That boiler is of the age that those things happened on a regular basis when it was installed, and your not having a proper high limit can cause you to end up as a newspaper story like these:

December 1933

January 1933

December 1932

switching the neutral is legal if it is interlocked. fusing it is not.

That bundle of white wire hanging from the ceiling looks suspiciously like old telephone wiring. Wonder what it is… or was…

This does not relieve you from having a high limit. It was the code when the gas burners were installed and it is code today!

"from what I read and even Dan’s videos and books, that was always a steam boiler issue."

That is all well and good, but I have witnessed a gas furnace with a runaway gas valve.  I got a call from an absentee customer that his vacation home in Avalon NJ, had a gas bill that seemed a little high.  After getting the key from the real estate office I entered the home to find that it was about 92° inside. (outside was 35°)  there were candles that had melted over and the electric switch would not turn off the gas.  That valve was stuck open and the burner was at a full tilt 110,000 BTU flame inside.  

Now think about that happening to your gas valve, which is similar to the one in my example above.  Your gravity hot water boiler might turn into a steam boiler in such a case. How does that pan out with all that mercury in that Honeywell No. 1 device work in that scenario?   

Of course that would not be solved by a high limit control, but if the thermostat wire happened to get a staple or nail to cut thru the insulation and caused the electricity to keep the gas valve open, even after the room temperature increased above the set point, you could experience that same hot water boiler making steam.  Your high limit would prevent that!   That is the reason for the high limit.  

I also had a prospective customer in Stone Harbor, NJ with a hot water boiler that made steam.  It blew out a 12” x 14” piece of cast iron that blasted thru the steel covering and made a 3” deep impression in the boiler room wall made of cinder block.  I wanted them to purchase a new oil burner to retrofit their 50+ year old hot water boiler. That cost half as mu h as a replacement boiler.  Four weeks later I got a call from that customer asking if it could be fixed. And could I put in that oil burner job.  

With half of the end section of the boiler missing, they needed to get the new boiler so another plumber got that job.  If he only decided one week sooner, he could have saved $$$ because my replacement oil burner job includes a new combustion chamber, new barometric draft regulator, new thermostat and new boiler operating and limit controls. Basically a new boiler operating system installed in that old boiler (like your old boiler).  The reason for the exploding boiler was a control issue and a plugged relief valve. That would have been solved with the work I would have done.   So that was never a customer of mine. 

Sincerely

ED Young

PS:

None of the explosions in the three 1932-33 stories above were steam boilers. The first was a furnace and the second and third were water boilers, LIKE YOU HAVE.

Those stories were from this book HeatingHelp.com/documents that had 30 or more boiler explosions listed. One story listed there were 5 explosions in the same week, two of those were in the same town. You have an old boiler and your want to keep it. make it safe to keep!

You can do the experiment by turning the thermostat uo to call for heat right now. the burner should start. Then you lower the Aquastat as far as you can, and the burner should stop. If that test does not work, then you may need to wait for the boiler temperature to increase and see when it stops. If the boiler temperature goes above the Honeywell Aquastat setting by more than 10° and the burner continues to operate, then that High Limit is disconnected. That is DANGEROUS!!!

Also, a water boiler does not usually have a pressure limit control. Do you believe that your have a pressure switch? Can you show me what you believe is the pressure switch?

You do have one switch that can be disconnected. It is the BASO switch. BASO is a brand name for the gas pilot safety switch. That switch is no longer connected to the pilot because that safety device is included in your upgraded Redundant Gas Valve. The old gas valve and pressure regulator gas train was replaced some time ago with a modern redundant gas valve that is designed to turn off the pilot gas if the flame goes out. The old Gas Train would allow the pilot gas to continue if the flame blows out. That was not a problem when that burner was installed but it will not pass code today. Since you already have the better gas valve you no longer need the BASO switch.