Can a Plumber Fix a Boiler? What They Can and Cannot Touch

The short answer: it depends on the registration, not the job title

In Great Britain, anyone who works on a gas appliance or gas pipework in a home has to be Gas Safe registered. That covers servicing, repairing, replacing parts and installing, and it applies to the individual doing the work. It does not matter whether their van says plumber, heating engineer or gas engineer. Plenty of plumbers are registered and fix boilers every day. Plenty are not, and they are perfectly good at the rest of the system.

Registration is also split by appliance. The category that matters for a boiler is the one covering central heating boilers and water heaters. An engineer registered only for cookers and fires is on the register and still not qualified to repair your combi. Our guide on how to check a plumber on the Gas Safe Register shows where to find that category on the card and how to confirm it online in under a minute.

What any competent plumber can do without gas registration

A lot of what people describe as a boiler problem is actually a problem with the water side of the heating system, and that side is ordinary plumbing. If the work happens outside the boiler casing and does not involve the gas supply, a plumber without gas registration can do it.

• Topping the system back up through the filling loop when the pressure has dropped
• Finding and repairing a leak on the radiators, radiator valves or heating pipework that is making the pressure fall
• Bleeding radiators, balancing them, and replacing radiators or valves
• Cleaning a magnetic filter, and draining and refilling the heating system
• Replacing a motorised zone valve or an external pump on a system with a separate cylinder
• Work on a vented hot water cylinder, the cold water tank in the loft and the feed and expansion tank
• Anything on the taps, showers and pipework that the boiler supplies

What only a Gas Safe registered engineer should touch

Treat anything that needs the boiler front off as gas work. A modern boiler is room sealed, so taking the case off disturbs the seal between the flame and your living space, and the parts behind it, from the fan and gas valve to the pressure relief valve, the diverter valve and the heat exchanger, all sit inside that sealed box. A plumber without registration should stop at the casing even when the part they are after is a water component.

• Any repair inside the boiler casing, including the diverter valve, internal pump, pressure relief valve, plate heat exchanger and expansion vessel
• Fault codes and lockouts that do not clear after one reset
• Anything to do with ignition, the flame, the gas valve or the flue
• The gas pipe from the meter to the boiler
• The annual service, and the landlord gas safety check
• Fitting, moving or replacing the boiler itself

If you can smell gas, this is not a question of which trade to call. Turn the gas off at the meter, open the windows, do not use switches or naked flames, leave the property and ring the National Gas Emergency Service on 0800 111 999.

Plumber, heating engineer or gas engineer: what the names mean

None of these titles is protected. Heating engineer usually means somebody who works mainly on boilers and central heating, and most of them are Gas Safe registered because the work is hard to do without it. Gas engineer normally means a Gas Safe registered engineer, although gas work also covers cookers and fires, so it still says nothing on its own about boilers. Plumber covers everyone from a specialist in bathrooms to somebody who does boilers all day.

Because the words are used loosely, go by the card rather than the advert. A registered plumber with the boiler category is as qualified to repair your boiler as anybody calling themselves a heating engineer. An unregistered heating engineer is not, whatever the van says.

Which one to call for the common boiler problems

Most calls fall into a handful of symptoms. This is roughly how they split between work a plumber can do and work that needs gas registration. It is a guide rather than a diagnosis, because the same symptom can start in either place.

• Pressure keeps dropping: often a leak on a radiator valve or pipe, which is plumbing. If the system is dry and the pressure still falls, the internal expansion vessel or relief valve inside the boiler is the likely cause, and that needs gas registration. If it has gone the other way, our guide on boiler pressure too high covers the causes.
• No hot water but the heating works: no hot water from a combi boiler usually means the diverter valve or the plate heat exchanger inside the boiler, so gas registration, and our guide to diverter valve replacement cost explains what that repair involves. On a system or regular boiler with a cylinder, the fault is often a zone valve, the cylinder thermostat or the cylinder itself, which is plumbing and controls work.
• Boiler locked out: one reset is reasonable, and how to reset a boiler explains the safe way to do it. Repeated lockouts are a fault inside the appliance.
• Water under the boiler: could be a joint on the pipework below it, which is plumbing, or the discharge from the relief valve, which points to a fault inside the boiler.
• Radiators cold at the top or cold in one room: air or balancing, which is plumbing.
• The boiler will not fire at all with gas at the hob: an internal fault, so gas registration.

Where the hot water cylinder fits in

If your hot water comes from a cylinder rather than a combi, part of what looks like a boiler problem may not involve the boiler at all. An unvented cylinder, the sealed mains pressure type found in a lot of London flats and conversions, is covered by a separate qualification, not by Gas Safe. A G3 qualified engineer holds that certificate. Gas registration says nothing about it either way, which is why we cover it in a separate guide on how to check a plumber is qualified for unvented work.

The immersion heater is different again. It is an electrical element in the cylinder, so replacing one is plumbing and electrical work rather than gas work. When the boiler has failed and the immersion still works, it is often what keeps a household in hot water until the repair, and immersion heater repair is one of the most common jobs we are called out for alongside a boiler fault.

Save a visit by describing the fault properly

The quickest way to get the right person is to tell whoever you ring exactly what the boiler is doing. Give the make and model from the front panel, any code on the display, the pressure on the gauge, whether you have a combi or a cylinder, and whether the heating, the hot water or both have stopped. That tells a good firm in one phone call whether they need to send somebody registered for the gas side, and whether it is worth booking a boiler diagnosis rather than guessing at a part.

Ask for the engineer's licence number too, and check it when they arrive. That applies to us as much as to anybody else. Any engineer who works on gas expects to be asked and will not mind.

If you would rather we sorted out which it is, ring us on 020 4652 5111 or send an enquiry with the details above. We work on the boiler, the heating and the hot water side, so you do not have to work out which trade you need before you call. What we charge is set out on our pricing page and agreed before anybody attends.