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Thanks, Ed. That was exactly the kind of info I was looking for. This boiler is built like a tank, and if all the parts that you mention could be replaced I bet it could last another 25 years and still be safe. I've been taking it apart for 25 years, cleaning it, and putting the burners back. Replaced the thermal couple and that gas shutoff valve with the tiny shutoff valve for the pilot. (I found a supply house that sold me a NOS replacement — he said that design is no longer code but the old one was leaking so it needed to be replaced) My initial inclination was to repair the boiler because a new one is never going to last as long as this one has. But I've come around to the idea that it's had a good run and it's time for a new one. (I may still ask contractors if they'd replace the parts with that kit for curiosity) I talked with one contractor on the phone who told me a 94% efficiency boiler needs lots of maintenance and only lasts 15 years and a new cast iron 84% will last 25 years. I don't know exactly how old this boiler is but it's at least 60 years old. New stuff isn't made to last like this anymore.

If you have this information ready for an experienced gas heat technician, you can ask them what it might cost to remove the old standing ignition parts and install this electronic ignition kit to make the old boiler more reliable. Y8610U Kit

It will replace all the parts in this photo

There may also be a 1/4" aluminum pilot tube that comes from the manual shut off valve the will need to be removed and capped off. This is the Cadillac repair, however there are less expensive repairs available. Just remember the price you pay at SupplyHouse.com is the wholesale price and if the contractor provides you that kit. It will be marked up and include labor to install the parts. It is a time consuming job and will also need additional parts and fittings to make the piping connections. The professionals are entitled to make a profit on both the parts and labor they pay the technician. So don't be shocked at the total price. Safety with a guarantee is worth the cost in my opinion.

Since I cleaned the sticky solenoid switch it has cycled on and off several times on its own and is working fine,

I have a problem with that statement because of this statement:

This doesn't happen every time, but it has been happening more frequently lately. The radiators heat up and the gas continues to heat the boiler even when I turn off the thermostat…

If the boiler is that old that the most important part of the safety devices on this boiler is failing dangerously more than once, what is to say that some other old part will not fail. What if the relief valve happens to be the part that fails? What if it happens at the same time, when you can't be there as a result of an unscheduled event that takes you away from "If I don't notice that the gas has not turned off," because you are hospitalized or at a funeral or your Lottery ticket that wins takes you the the Governors Office for "photo-op"

What happens to this water heater, could happen in a very short time with your boiler.

This water heater is only 40 gallons of water, and it happened in less than one hour. Your heating boiler with all the radiators has much more water and therefore much more explosive force when something gives way, and all that water that is over 300 PSI and end up well over 400°F, rapidly changes to steam as the pressure drops to zero PSI where 400°F water flashes into steam instantly, and becomes 1700 times larger than it was when it was water.

To put this in perspective. TNT increases about 900 times its size when it explodes. Water becomes 1700 times larger when it explodes. That is almost two times the explosive power that Dynamite!

As a person that has no training on how to play with fire inside your building, can I suggest that you SHUT THAT BOILER OFF NOW and listen to the professionals who have been trained in this "playing with fire" in your building, while you still have a building.

Just some ramblings from an old guy with over 40 years in the trade. Probably worthless information. But If it were me… I would aer' on the side of caution

It should have a taller riser, ideally around 8"-10"

It'll likely possible to replace the gas valve & ancillary parts with modern components, but it may take some looking to find the right person to do it. Try the "Find a Contractor" link in the blue bar above.

Given the age, replacement might be the correct answer.

You still shouldn't operate it until it has been serviced. Gas stuck on is a serious failure. If the pressure relief fails, a boiler explosion is the next step.

Being as it's a boiler & not a furnace, it may be worth the effort to find someone to replace the gas train. You'll have to work to find the right person, but you might come out in the black.

I'm glad you understand that there are risks here.

That is a very dangerous condition. You need to immediately turn off the gas and electricity to the boiler & call to get it serviced before you end up killing yourself or someone else.