I'm late to this post so I'll keep it brief - nothing other than wall removal would bother me. You know, if the boiler was condemned just get a new boiler. I've not had mine serviced for ages - sometimes when you're a home owner you get lazy with stuff. That wouldn't bother me. I have a steel beam holding up 3m of my rear first floor and I've discovered recently that there is so much more to it than I'd thought. I wanted to take it across 6m and had one structural engineer tell me that we couldn't do it because the weight of iy would be too much for the existing foundations to take. Another one said that there'd be no problem at all. As you say in your initial post, no-one goes to the time, trouble or expense of putting in an RSJ if they don't need to. If they've taken out a stud wall you don't put an RSJ in. It suggests to me that it has to be load bearing and then you get into the realms of whether the steel is big enough and position right to support the load above it. If it is, is the foundation strong enough for the weight if steel? That's why building control exists and this work shouldn't have been done without building control approval. If anything is wrong you lose a wall, hopefully no one is hurt. Then you have the aggro with the insurers etc. Or alternatively, the structural engineer says that there's absolutely nothing wrong with it and you should be fine. Who pays for that? You tell him you want him to pay and he says "no". Your choice is either you walk away or you pay. I'd walk away personally, but it's a choice of heart v money.
To be honest I'm looking to getting it serviced now - I thought after typing that I probably should!!