Plumbers in the developed world are required to undertake jobs only which they are fully qualified to do. For example, many plumbing and heating courses now include gas training which means that your plumber could carry out tasks in your home or office which are covered under the skill-set they hold. Many plumbers out there do not realize they could significantly upgrade their profits by undertaking a gas course to compliment their skills in heating and plumbing.
As heating and gas are dangerous aspects of home repair to be around, the pay structure you offer will change. Usually in business it is great to have a niche, but being only a plumber or only a heating specialist blocks out the avenues which could lead to more work. Your niche as a plumber has now just been extended to being able to carry out gas and heating supply jobs too.