I had an earlier post about fixing the flue collector, which I have done pending having a new one made next summer. No CO alarms are going off and no odd smells relative to leaks (realizing that I can't smell CO itself), so I think it's good for now.
One person said a gas boiler should never need cleaning (should never soot up) however while I believe this may be true of new boilers, the old boilers clearly required cleaning because there is a factory sticker on it saying it must be cleaned every year, so it was expected that they would need cleaning.
What I do is make sure the area of the boiler tubes is as clean as I can get it using something to poke down in there that will not injure the tubes, try to get off all loose debris, and vacuum it very well. It should be possible to shine a light down from the top and see the openings are free and clear. If they are not, this will certainly contribute to sooting up.
The other thing that contributes to sooting is if the burner tubes are not clean. When the boiler tubes are cleaned, debris falls onto the burner tubes and must be removed. I use soft plastic tubing with the end cut at an angle and go in there gently and remove all debris from the tubes and underneath and between and anywhere there is any debris at all. This should result (and did) in getting blue flame everywhere and there should not be any place where there is any or very much at all of yellow flame because that is the incomplete combustion causing sooting. I believe that the cleaner everything is, the less it will tend to soot up, and with a maintained boiler, once a year should be fine. It is however easy to take off the burner tube cover and take a quick look to see that the tubes are operating properly.
I imagine at some point the burner tubes will wear out and have to be replaced, and I think that would be obvious by the fact that they are very clean yet do not have a nice blue flame. There is an adjustment for the tubes, but I do not mess with that at all. I understand that with the right instruments there are kinds of tuning that can be done, but if the flame looks good, I have no reason to think they would need adjustment.
This is mostly for the d.i.y. people - it's not that hard to do a good cleaning job. I use a shop vac with a dust bag in it. I'm sure the pros have specialized equipment, but if you have some narrow attachments, and some tape to attach some soft tubing, you can do a really good job. A very bright light is helpful if not essential.
The effect of never cleaning is that eventually when the boiler lights, the flame will come out the front of it, and when I originally moved here that was the situation because the boiler tubes were completely blocked. That, along with replacing the thermocouple and drain valve and pressure/temp gage, got the thing going, and I've patched the flue collector a couple times now so that needs to be replaced (have to have one made). Otherwise, there's no reason it can't keep running. As long as it doesn't leak (water - or exhaust!), then it seems that pretty much everything else on it can be replaced.
I realize newer boilers are much more efficient and at some point that will happen, but probably not until something happens that can't be fixed. I don't think the payback is there for the increase in efficiency, but I could be wrong.
The boiler is, I believe, from the 1960's era, perhaps a bit later.
I made a change in the circulating pump settings. I had it set at 130 which resulted in circulation 145 down to 115F. I changed it to 145 resulting in high/low of 160 and 130. I based that on reading somewhere that below 130 boiler temp can cause condensation and although I don't understand the cause or effect of that, the higher circulating temperature seems to work fine. I had lowered it at one point feeling that it caused more even circulation to the distant radiators, but if that were even true, I think the higher run temp is probably better, unless I hear differently.
I appreciate the many comments and assistance and I welcome additional comments.