Interestingly, there’s a big difference. They are completely different trades. So it still comes as surprise when I hear the two words used interchangeably when people refer to my trade. I am a gas engineer based in Essex and London areas, and specialise in domestic gas services. To clarify further, this involves any work relating to gas boilers and gas central heating. That means working solely on the heating of a building, and installing and maintaining the appropriate fittings, pipework and infrastructure. However, as part of studying to qualify, I was required to undertake a basic plumbing course, although I would not be able to call myself a fully experienced plumber, as the range of work undertaken by plumbers is so broad. Plumbers do not need any formal training or qualifications, and can qualify through experience. Gas engineers on the other must hold the formal qualification as well as be Gas Safe registered. It is a highly regulated industry, and rightly so.
This leads me to what a plumber actually is, which is “A person who fits and repairs the pipes, fittings, and other apparatus of water supply, sanitation or heating systems.” In the Roman times, plumbers worked with lead pipings, and the Latin work for lead is “Plumbum”. You learn a new thing every day! So there’s quite a clear difference.
It’s seems that the confusion stems from the fact that many plumbers also train and qualify as a Gas Safe engineer in domestic gas work, as well as plumbing. So it’s can be quite common for a tradesman to specialise in both fields. But just for future reference, if you need any gas work undertaken, it may be wise to call a gas engineer and not a plumber in the first instance, and vice versa!