To be honest I admire anyone that's willing to take the jump from a full-time job into our market. That said, I do think it's important to be realistic about the opportunities these courses offer you. As the people who've been on this forum for a while know, I'm one of those people who career changed in my late 20s and did a 'fast-track' plumbing course to kick start that. It was 6 weeks full-time with OLCI, basically teaching me to C&G Level 2 in Domestic Plumbing. The course was as thorough as a classroom based course could be in that time. BUT, what it didn't give you was the most important part - EXPERIENCE.
If you want to install gas boilers, how will you do this with no plumbing experience? Rightly or wrongly, customers expect gas fitters to be able to install all aspects of plumbing related to boilers. For this reason I think people who do gas courses first without a good 5 years or so of plumbing experience are madder than a box of frogs.
If going the fast track way, here is the proven way to do it: -
1.) Spend your money on a fast track course that qualifies you to C&G Level 2 in plumbing. You may decide to find a provider that offers NVQ assessments when you start fitting bathrooms etc. Only really necessary if you want to work for someone else essentially. You don't need a NVQ if you are going to work for yourself.
2.) Start up your own business. Make sure you have a local contact - an experienced plumber, you will be calling on them and passing them a fair few jobs to start with!! To start with, limit yourself to the jobs you feel confident to do. Tap replacements/repairs, toilet repairs etc. If you get anything you're not sure about, pass the work to your contact - he gets paid for doing it and you watch and learn. This way the customer remains yours and you are gaining valuable experience. He gets paid for the job so it's win win.
3.) As you get more confident you will be passing the contact less and less work. Always be aware of your limitations and grow the business from there. After about 5 years you will be comfortable with most domestic plumbing issues that crop up. This is the time to start looking at gas courses!!
Gas should be the icing on the cake, the last thing a plumber qualifies on in his career. So many boiler faults are actually down to plumbing issues. Without experience of this, you become just another fast-track clown who actually has no clue how to do anything.
When I did my portfolio I was trained by one such person to start with. I moved to a more experienced gas engineer as soon as I realised I actually knew more than he did!!
Experience is everything in this game and qualifications count for very little.
Unfortunately it's fairly well known that plumbing on it's own doesn't make you that great a living. The money is definitely in doing gas work. The main reason for this is that every boiler you fit should (if you've done a good job) guarantee you repeat work every year through the annual service. Every gas fire you fit, the same. That's not the case with plumbing, it's usually replace a tap and then you won't hear from the customer for a good while.
The above fact doesn't mean you should jump the plumbing side. One leads into the other!!