Thought I would chuck my two pence worth in, as I feel Im in a good position to answer to this post.
Im in the minority as I did my apprenticeship doing commercial gas and heating installs and gained my COCN1 before domestic.
As has been previously said, most of the places that have commercial equipment inside it will already be looked after by FM companies. I currently work for a large multi-national construction company who have a contract to look after a brand of banks within the UK.
I live in Blackpool and know for a fact, that the majority of hotels around this area have contracts with maintenance firms that I couldnt hope to compete with if I was looking for the work on my own.
I think unless you're confident that you will get some work which could then lead on to more work, its an area which has already been snapped up by large companies.
I have used my commercial gas since I was an apprentice, but only used it when working for the few companies I have worked for, On my own I have only ever done one job, It was a boiler room refurb in Bolton that required two new boilers and two new Andrew water heaters. The only thing that was asked for was for it to be done in iron pipework, in my eyes there was more work involved with this than if it was just a small domestic boiler room, I managed to get it done but it was hard work.
I also find that with commercial pipework, both gas and heating, the actual systems are fine and will run forever its more the appliances that require the maintainence, so you then need to think about what area of work would you be looking in? Maintenance? Full installs?
This then comes down to personal ability. If its boiler maintenance and repairs then everyone would most likely be ok, if you get contracted to do some install work, say a new boiler room that needed doing in iron pipework how would you cope with that? Going from domestic to commercial, is in my eyes harder than going from commercial to domestic.
I know a few domestic lads that dont know how to work a screwing machine, on the other hand I know a few lads who can use one easily.
Please dont take anything I have said as personal dig, its just that for the price of doing the commercial assement I would hate for you to spend the money and expect a decent return both easily, and quickly.
Obviously you could get lucky and do one job right away, word of mouth gets your name around even more as a commercial company and you make a good bit of money, but as thats not likely I think you need to be objective about the way you look at this.
Whatever you decide, best of luck!
Here is a small photo of the only commercial job I have done, 90% of this job was done in iron. There were two more water heaters behind me with a BMS system on the wall.