Heating System Problem

I’m having problem with a house I recently purchased, which we haven’t yet moved into. It’s a 1920’s wood frame Dutch Colonial with mostly original steam forced air radiators. We did and oil to gas conversion over the summer. When we first started using the new heating system, we noticed an odd smell coming from some, but apparently not all of the radiators. But hard to tell because the fumes travel from room to room. I don’t know how to describe it – it’s some kind of fumes, sort of a chemical smell. It’s pretty strong in some rooms. The company that did the oil to gas conversion, which is one of the top heating companies in the city with a lot of experience, came over to check it out and they are stumped as to what it is or what’s causing it. They said they’ve never had that kind of smell or that kind of problem before with radiators. They flushed the system and skimmed the boiler – twice and there is no improvement. Next, I asked them to try swapping the radiators from room to room, so we can isolate if it is an issue with particular radiators or particular pipes. Ho ping to have that done next week. We first came to see the house last winter and had the inspection done then and the (previous) heating system was on those days and there was no such smells from the radiators. Oddly, it seems to be mostly coming from what looks like the oldest radiator in the house in the living room, as well as what looks like a newer one in one of the bedrooms. Our contractor also can’t figure it out. Any ideas? Anyone ever have a similar problem with their heating systems? Anyone know if there are any city or state agencies/programs that will do air testing for us, or a private company that you would recommend to do air testing? Then maybe if we know what it is we can work backwards to figure out what is causing it. I’m going to try asking DEP next week. Any suggestions, please let me know. Thanks.