Best Of

Steam leaks in mains do happen and if un insulated chances are higher . If insulated look for spots that the insulation is stained or falling off clear sign there’s a leak . As for pressure testing it can be done ,remove all air vents and plug remove main vents and plug and pressurize I would say only to a max of 1.5 to 2 psi that’s it no point and in going higher system should never see that hi a pressure . I would think the easiest way would be to have ultra sonic leak detector , which should be able to pin point it . I don’t have one but it’s on the wish list reason being I have a few refregerant leak dect. And have found for refrigerates I haven’t had a need for an ultrasonic leak dect for refregerants yet but like I said in the works $$$
You should take a good look and see if there are visible signs of leakage from radiator vents and radiator supply valves . If going a replacement boiler be sure it’s sized to match the existing edr and if you have wet returns take my advise if zero maintaince has been the mantra do ur self a favor and have the wet returns checked out and even if replaced have isolation and purge valves installed ,you will be needing them to flush out everything that will end up there . One final note if hiring some one make sure they know what there doing not just a sales guy ,you want a owner / operator to do your replacement ,this way it ain’t just the sales guy w a pitch and commission and a lower price and then your looking for some one else to finish what there price did not include . I see it all the time lol
Being the home is in heating disrepair don’t think it will be cheap in this day and age . Aside from proper boiler piping and sizing ,a true steam boiler upgrade in my eyes includes new radiator vents and main vents and I hear it all the time that there new ,that’s fine cause if they don’t work and it’s not priced in you pay extra If none of that is included in my eyes you need a different contractor being without these items a properly operating would be crap shoot and there’s be extras like re do the rad vents and mains . Again take all w a grain of salt I tend to tell the truth and this is it as I see it . Get one guy make sure he s not full of Pooh so there’s no bs and check his references .
I know this as a noble truth because i see it all the time 1/2 butted jobs and they except it all straighten for peanuts lol myself I’ll hang out at home eating peanuts before I work for nothing for those looking for a bargain ,if so you got the wrong tree to bark up .In general stay away from franchise bossinesses in my experiences it’s always a half a mech doing the work and the future of workers now a day are beyond lazy just looking at a cell phone and getting home and usually milking any job they do cause nobody likes getting back to shop early to be sent out again .More concerned about there life then your heating system . Again one of the four noble truths according to the clam .
Remember steam is pretty easy w just about zero moving parts aside vents and gas valve it’s not that hard so any one who shows up in sneakers w clean hands and good back should be shown the door espically sneakers
Take it all w a grain of salt ,only the truth
Peace and good luck clammy
The sweetening of a cheaper price is soon forgotten after the bitterness of poor quality .

I'll play devils advocate here. We Americans preach to one another about the need for high efficient everything, from our electric appliances, automobiles and most especially our heating/cooling systems. Then we come across these antiquated steam systems with their 100+ year old radiators and we just seem to forget about efficiency because the rads look so "neat" or "artistic" and it seems we must keep them in service no matter what. These systems represent an era long, long gone!! It's time to update that old steam system to something more efficient, that goes for ALL steam, everywhere except perhaps in an industrial application that requires steam like mushroom farms or papermills. Yes, it might cost an arm & leg but isn't our future worth that? It's not going to get any cheaper!! If you really love those old radiators, pull them out and put them in a museum where they belong on display for the by-gone times of ancient
heating. Bra-ha-ha-ha!!

Interesting that you would blame the emitters for the efficiency of this system not knowing what the source is. Sure we can make assumptions but should we? There are not too many more efficient ways to store and deliver heat energy than high mass cast iron emitters. We really should be picking on the building envelope, though we can only assume what that is.