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did use thermocouples of what later became the standard type. On these, the thermocouple held a switch closed so the 24-volt current could reach the main gas valve. If the pilot went out, the switch opened and the main valve couldn't respond to the call for heat. BASO was a very popular manufacturer of this type of equipment. Some later versions would shut the pilot off too as well as the main valve, but these aren't as common. You'd need a knowledgeable heating man to recognize what you have and why it keeps going out.
If you have an ancient "gas train" (which term covers all the controls that regulate the gas on your boiler) and the boiler is expected to remain in service for a while, it makes sense to upgrade to the current type of gas train equipment. This way you're much less likely to have problems, and if you do they will be more easily fixed.
There is also the possibility that the gas train is not the culprit here. During the winter, gas pressure can fluctuate enough to kill a pilot light, especially on older gas distribution systems. Also, I've seen cases where there was an obstruction in the gas pipe coming in from the street, and when the boiler tried to light off the gas pressure got so low that the flame would sometimes snuff out before it could catch fully, taking the pilot with it too. Both these situations are the gas company's problem.
Again, you need a real good gas tech here. Try the Find a Professional page of this site.
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