Best Of

If you have been in the house for a while you probably have some experience with what percentage of the time the boiler is firing during the coldest weather. If it’s firing 75% of the time or more during the coldest nights, don’t reduce the size. If it’s firing continuously and the room temperature remains below setpoint increase the size.

If you’re new to the house, I suggest having someone clean it and adjust the burners. Some of the cast iron boiler designs have a very long lifespan, some fail very predictably at 7 years or 14 years, etc. The boiler has been there for quite some time, it may be one of the designs that lasts indefinitely. Since you would replace it with a non-condensing boiler, there isn’t a significant efficiency gain or impressive technology update. Don’t express an urge to replace the system to your heating professional at this point. Many heating professionals will interpret that to mean that you’re hoping they can find something that helps you justify the expense of a new system to yourself even if they might otherwise say it’s aging well and will last at least another 5 years. If there’s any sign of a boiler leak or burner defects or other significant problem they’ll tell you.
Every boiler manufacturer periodically loses control of the quality of their grey iron casting line and the boiler sections have excessive internal stresses and/or material consistency issues. The result tends to be boilers that leak and fail in much less than 20 years. Sometimes just 2 to 5 years. Since your objective is reliability my suggestion is to keep an eye on the casting you have and when it needs to be replaced look for one from a manufacturer that hasn’t had any models with problems in the last 10 or 15 years. Don’t consider a sheet steel boiler instead of cast iron, there are a different set of problems that limit their working life. There have been good welded steel plate boilers made or imported from Europe in the past. I’m not aware of any being widely marketed for gas burners right now, but I don’t follow it that closely.

" let me ask you this…if i were to start replacing parts, assuming something has failed, where would you start? "

check for 120v at the higher red circ, or from its controller(back of boiler) and the green one at the ceiilng also, if they have power, then the circ is bad, or jammed,

you mentioned the water was dirty, dirty water might have seized the circ(s),

the red one, isolate the circ with the valves above and below as you did earlier, on the end of the circ motor, that screw head, take it out, expect minor water, see if you can turn that shaft inside there to free it up or prove loose, put screw head back in.

may be able to do same on upper green circ,

if you don't have 120v at the circs, you have a controller or thermostat problem, did you check batteries at the stats?

purge on the boiler screen is part of the ignition / burn / shutdown sequence, not what we're looking for,

purging air from the zone loops is playing with all your valves, a hose, and forcing water where air should not be,

you need to figure why the circ(s) aren't circing,

one must be working in that your domestic hot is working,

can you post one distant picture showing the whole deal down there, floor to ceiling, left to right,

dirty water is better than air

up at the ceiling,

the big green thing is an expansion tank,

to the right of it I see a small red tee handle on an open drain, it's a 1/4 turn to full open, careful now,

just nudge it open and see if there is air there, a bucket is your friend,

and there is a picture of one end of your baseboard, are there any other fittings at the far end, an air valve or vent?

is it in outdoor reset?