Guide
Plumber or heating engineer: what each one does
A plumber moves water. A heating engineer works on the boiler and the system that heats it. Gas work needs Gas Safe registration, and that is the line that matters.
The short answer
A plumber installs and repairs the pipework that brings water in and takes waste away: taps, toilets, baths, showers, sinks, drains and the pipes between them. A heating engineer works on the system that heats the water and the house: boilers, radiators, cylinders, controls and the gas supply that feeds them. Most working plumbers do a good deal of both, and many heating engineers came up through plumbing.
The line that actually matters
The real division is not the job title, it is the registration. Any work on a gas appliance or gas pipework in the UK must be done by an engineer on the Gas Safe register, and the register is per person and per category. A plumber without it can fit your radiators, run your pipework and plumb in your cylinder, and cannot legally touch the boiler.
So the question to ask is not whether somebody calls themselves a plumber or a heating engineer. It is whether they are Gas Safe registered, and for which appliances. The register is public and free to search, and the card an engineer carries lists the categories on the back.
Which one do I need?
If the job involves gas or a boiler, you need Gas Safe registration, whatever the person calls themselves. If it involves water, waste or drainage and nothing burns anything, an unregistered plumber is entirely appropriate and often cheaper.
Unvented hot water cylinders are a third case. They need a separate G3 qualification, which is not the same ticket as Gas Safe registration, and a plumber can hold one without the other. If a cylinder is part of the job, ask about G3 specifically.
What about gas engineers, and drainage specialists?
Gas engineer is the same trade as heating engineer in ordinary use, though the phrase is also used by people whose work is cookers, fires and meters rather than heating. Commercial gas is a separate set of categories again, and a domestic boiler engineer is not qualified for a catering kitchen.
Drainage sits slightly outside all of this. Firms with jetting units, CCTV survey equipment and excavation capability are drainage contractors rather than plumbers, and for a recurring blockage or a collapsed run they are the right call.
Common questions
Can a plumber work on my boiler?
Only if they are on the Gas Safe register. Plumbing qualifications alone do not permit gas work, and the register lists which appliance categories each engineer is signed off for.
Is a heating engineer more expensive?
Hourly rates are similar. Boiler work costs more because the parts cost more and the jobs are longer, not because the trade charges a premium.
Who do I call for a leaking radiator?
Either. A leaking radiator or valve is water, not gas, so any competent plumber can deal with it.