G3 Qualified Plumber in London

What does a G3 qualification actually cover?

G3 is the hot water systems assessment covering unvented storage over 15 litres. Holding it means the engineer has been examined on how a sealed cylinder keeps itself safe, how each of its protective devices behaves, and what to do when one of them has already failed. It sits apart from a general plumbing NVQ and apart from gas work. A very capable plumber who has never sat G3 is not qualified to commission the safety controls on an unvented cylinder, and most honest ones will tell you that themselves.

In practical terms the qualification covers installing a new unvented cylinder, commissioning it, servicing it, repairing or replacing its safety components, and decommissioning one that is coming out. That means anything touching the pressure reducing valve, the single check valve, the expansion vessel, the expansion relief valve, the temperature and pressure relief valve, the thermal cut out, the tundish and the discharge pipework. Those parts are what make a sealed cylinder safe, and they are the parts the assessment is built around.

It is also worth knowing what G3 does not cover, because that is where confusion starts. It is not a gas qualification, so the boiler that heats the coil is separate work. It is not an electrical qualification, so the immersion circuit and its wiring sit outside it. And it says nothing about vented systems, which are open to atmosphere through a feed and expansion tank in the loft and do not carry the same stored energy. A new unvented installation is notifiable work under the Building Regulations, which is the other reason the qualification matters when you come to sell the property.

Why it matters who works on a sealed cylinder

An unvented cylinder stores a large volume of water at mains pressure and well above 60 degrees. Water expands as it heats, and in a sealed system that expansion has nowhere to go except into an expansion vessel or an internal air gap. If that absorption has been lost, pressure climbs every heating cycle until something lets go, which is usually a relief valve doing its job and dumping hot water down the discharge pipe.

The system is designed with three layers between normal running and a dangerous cylinder. The control thermostat holds the temperature. Behind it, a thermal cut out drops the heat source out if the thermostat sticks. Behind that, the temperature and pressure relief valve opens on either temperature or pressure and vents to a safe place outside. Serious unvented failures are rare precisely because of that layering, and the layering only works when every part is present, correctly rated for that cylinder and actually commissioned. Remove one layer quietly and nothing appears to change until the day the layer in front of it fails.

That is the reason the qualification exists, and it is why an unqualified fitter is both a safety question and a paperwork one. The work we see go wrong is almost never dramatic. It is a relief valve swapped for a part with the wrong rating because it was the one on the van, a discharge pipe reduced in bore and run uphill, a tundish taken out to tidy a cupboard, an expansion vessel left uncharged after a repair. Each of those looks fine on the day. Each of them removes protection the next engineer will assume is there. Two of those failures announce themselves before anything serious happens, which is why a dripping tundish and a leaking pressure relief valve each have a page of their own here: the water you can see is almost never coming from the part that has actually gone.

If your tundish is running constantly, or the pipe outside is dripping hot water, treat it as a fault rather than a quirk of the system. Both mean the cylinder is releasing pressure it should not be building in the first place.

What to ask a G3 plumber to show you before they start

Nobody sensible minds being asked. A G3 engineer carries a card, it has a photo and an expiry on it, and checking that the name on it matches the person in front of you takes ten seconds. If someone becomes awkward about it, that is your answer. The same habit is worth applying to the gas side, where how to check a plumber on the Gas Safe Register is a two minute job against a public record rather than something you have to take on trust, and knowing how to check a plumber is qualified for the specific work in front of them is the part most people skip.

There is one honest grey area worth understanding. Not every job on or near a cylinder is G3 work. Changing a tap that happens to be fed by the cylinder is ordinary plumbing. Touching the relief valves, the vessel, the discharge or the commissioning is not. If a fitter tells you the qualification is not needed because it is only a small repair, ask specifically which components they intend to disturb, and judge the answer on that rather than on the size of the job.

• The G3 card itself, in date, with a photo that matches the engineer on your doorstep.
• For a new installation, the registration that allows the work to be notified, or confirmation that it will go through building control instead.
• Any manufacturer training they hold, where the cylinder is a branded unit with its own parts and procedures.
• The service record or benchmark book they will complete and leave with you afterwards.
• A clear answer on what they intend to do with the discharge pipe, before the work starts rather than after.

When you need a G3 engineer and when an ordinary plumber will do

Plenty of hot water problems have nothing to do with the cylinder safety controls, and paying for a specialist visit you did not need is a waste. The split is reasonably clean once you know where the line falls.

If you are not sure which side your job is on, describe the symptom rather than guessing at the cause when you book. Water dripping from a pipe outside a wall, a cupboard that smells hot, or a cylinder that overheats after an immersion has been on all night are all safety control symptoms. Slow hot water at one tap, a noisy filling, or a dripping shower valve usually are not. Once you know which side of the line you are on, the unvented cylinder installation page covers a new cylinder or a conversion from a vented system, the unvented cylinder service page covers what an annual check includes, and the unvented cylinder repair page sets out the faults we find part by part.

• G3 work: new unvented cylinder, replacement cylinder, annual service, relief valve leaking or weeping, expansion vessel replacement, tundish or discharge pipework alterations, cylinder overheating, decommissioning a cylinder that is coming out.
• Ordinary plumbing: taps, shower valves, isolation valves, pipework runs beyond the cylinder connections, airlocks, toilet and cistern work, stopcocks.
• Gas work: the boiler itself, its controls and its flue, even where the boiler is the heat source for the cylinder coil.
• Electrical work: the immersion circuit, its spur and its cable, though the immersion element and its own thermostat and cut out come back to the cylinder.

What our G3 engineers do on the visit

The order matters, because most unvented faults are pressure faults wearing a different costume. We start at the incoming supply, not at the cylinder. Static mains pressure and flow at the stopcock tell us whether the cylinder is being fed what it was designed for, and a surprising number of complaints about poor hot water turn out to be a partially closed stopcock or a failing pressure reducing valve rather than anything inside the cylinder at all.

From there we work through the safety set in sequence. The pressure reducing valve is checked against its setting. The expansion vessel is checked for charge and for a failed diaphragm with the system isolated and the pressure released, and is recharged or replaced on the spot where it has gone. The expansion relief valve and the temperature and pressure relief valve are both exercised and watched to see that they reseat cleanly rather than weeping afterwards, which is the most common thing a scaled valve does. The tundish is checked for flow and the discharge is followed all the way to its termination.

Then the heat sources. Where the cylinder is boiler fed we check the coil, the motorised valve and whether it is actually driving open, because a valve that has failed in one position produces a cylinder that will not heat while the radiators are perfect. Where there are immersion heaters we check the element, the control stat and the thermal cut out, and we look at the element itself for scale, which in London is the single most common reason an immersion stops delivering. Where the element itself has gone rather than the controls around it, that becomes an immersion heater repair, and our immersion heater repair page explains what changing one on a sealed cylinder involves. Finally we look at sediment and scale inside the cylinder and at the condition of the connections, and we write the readings down and leave the record with you.

Where the cylinder is a branded unit, and most in London are, the parts are not generic. Manufacturers specify their own vessel charge figures, their own relief valve ratings and often their own immersion elements with a particular length and thread, and a unit like a Megaflo has its own service procedure rather than a universal one. Fitting the nearest looking part is how a cylinder ends up venting on every cycle. Part of the reason we ask for the make and model when you book is so the engineer arrives with the right component rather than a close approximation, and so the record we leave matches what the manufacturer expects to see.

If we find something that cannot be left, we say so plainly and explain what it does and what happens if it stays as it is. If we find a cylinder that is safe but tired, we will say that too, rather than turning a service into a replacement quote.

• Incoming mains pressure and flow, measured rather than estimated.
• Pressure reducing valve, single check valve and strainer condition.
• Expansion vessel charge and diaphragm, recharged or replaced where needed.
• Expansion relief and temperature and pressure relief valves exercised and checked for reseating.
• Tundish and the full discharge route to its termination.
• Cylinder thermostat, thermal cut out, immersion elements and boiler coil performance.
• Written record of what was found and what was set.

A service means the cylinder is isolated and pressure released, so there will be a period with no hot water while we work. Tell us in advance if someone in the property needs hot water at a fixed time and we will plan around it.

Finding a G3 plumber near you in London

We run 20 engineers across London, and unvented cylinder work goes to the ones who hold the qualification for it. That is the only promise worth making about coverage: whoever attends your cylinder is qualified for the work described, and will show you the card without being pushed.

London property throws up the same handful of problems over and over, and they are worth knowing about because they change what an engineer looks for first. The water is hard across most of the capital, which scales relief valve seats, furs immersion elements and shortens the life of anything that sits in hot water. Period conversions often have a cylinder squeezed into a cupboard on an upper floor with a discharge route that was never properly solved, so the pipe ends up reduced, run the wrong way or terminated somewhere it should not be. Flats above shops and in purpose built blocks frequently have nowhere obvious for a discharge to go at all, which is exactly the situation where an unqualified fitter improvises and a qualified one stops and designs it.

Landlords and managing agents make up a steady share of this work, and the requirement there is usually as much about evidence as about repair. An unvented cylinder in a let property needs to be maintained and needs a record showing it was, by someone qualified to do it. We service on that basis and leave a written record of the readings and the condition of each safety device, so the file holds something more useful than an invoice. If you manage several properties, tell us when you book and we will keep the records consistent across them. What a landlord actually has to keep working, and how fast, is set out on our page covering landlord hot water responsibilities.

Older converted flats also tend to have a single cylinder carrying the entire hot water supply with no backup, which is why a failure there is urgent in a way a heating fault often is not. If you are in that position, say so when you book. It changes how we schedule and it changes what we carry.

What we usually find on cylinders fitted without G3

These are not theoretical. They are the repeat findings on systems installed or repaired by someone who was not qualified for the work, and most of them are cheap to have done properly at the time and expensive to unpick later.

None of these are difficult to correct in isolation. What makes them worth catching is that they compound. A cylinder with a flat vessel and a scaled relief valve has lost two layers at once, and nobody living with it would know until the day the thermostat sticks.

• Expansion vessel never charged or charged to the wrong figure for that cylinder, so the relief valve vents on every heating cycle and wears out early.
• Temperature and pressure relief valve swapped for a part with the wrong rating, or reinstalled with sealant on the seat, so it either weeps permanently or does not open when it should.
• Discharge pipe reduced in bore, run with a rise in it, or fitted with too many bends, so the valve cannot vent at the rate it was designed to.
• Tundish removed or hidden behind boarding, which takes away the only visible warning that the system is discharging.
• Discharge terminated inside a cupboard, into a soil stack without provision, or somewhere hot water can land on someone.
• No pressure reducing valve, or one left at the factory setting with no regard for the incoming main.
• No commissioning record at all, which means the next engineer has no baseline and the next buyer has no paperwork.

Booking a G3 certified plumber, and what helps before we arrive

Book through the contact page and describe the symptom in your own words. You do not need to diagnose it. What genuinely speeds up the visit is a few details that tell us what to put on the van, because an unvented job done in one visit usually comes down to whether the right vessel or valve was already on board.

On cost, the rate is fixed before we attend and does not change for an awkward property or an evening visit. The total depends on how long the job takes, and the pricing page carries the figures. A plumber call out fee is a charge for attendance rather than for outcome, which is why what it does and does not include is worth settling on the phone before anyone is booked. If a repair turns into a case for replacing the cylinder, we will explain why before doing anything, not afterwards.

• Make and model from the badge on the cylinder, and roughly when it was installed if you know.
• Whether the cylinder is heated by the boiler, by immersion heaters, or by both.
• Whether the tundish is running, dripping or dry, and whether the pipe outside is wet.
• Whether there is hot water at all, and whether the heating still works normally.
• Where the stopcock is and whether the cupboard can be cleared enough to get at the cylinder.