How to Check a Plumber Is Qualified for Unvented Work

What qualification does a plumber need for unvented hot water work?

A separate competency certificate for unvented hot water storage systems, held by the individual engineer, assessed at an approved centre and time limited rather than held for life. It is not part of a plumbing NVQ, not part of gas registration, and not granted to a company. One sentence on the regulations and then we will leave them alone: this sits under Part G of the Building Regulations, which is why you hear it called G3. In practice somebody searching for a G3 qualified plumber means exactly this certificate, so the shorthand is fair enough even though the paper itself says unvented hot water storage.

What matters is what the certificate is actually about. It covers the safety chain on a sealed cylinder: the pressure reducing valve and its setting, the single check valve, the expansion provision, the expansion relief valve, the temperature and pressure relief valve, the thermal cut out, the tundish, and the discharge pipework that carries released water somewhere safe. Those parts are the reason a mains pressure cylinder full of water above sixty degrees is a boring object rather than an interesting one.

• Held by the individual engineer, not by the business that took your booking.
• Time limited, with an expiry printed on the card, and reassessed rather than renewed by post.
• Separate from a plumbing NVQ, separate from Gas Safe, separate from electrical competency.
• Needed to install, commission, service, repair or remove an unvented cylinder and its safety controls.

What the unvented certificate looks like and what to read on it

Most engineers carry a wallet sized card with a photograph, the full name, the awarding organisation or scheme, a unique certificate number, an issue date and an expiry date. Behind the card sits the paper certificate naming the assessment centre and the unit assessed. Read the name, the expiry and the number, in that order. The rest of the card is presentation.

Several awarding organisations run the assessment, so different logos are normal and are not a warning sign. What is not normal is a card with no number, no expiry, or no issuer named anywhere, because a card that cannot be traced back to somebody proves nothing. Watch for two things offered as substitutes: a manufacturer training certificate, and a trade association membership logo. Both are legitimate objects. Neither is the assessment you asked to see.

A certificate that expired last month with a renewal booked is not the same as a current one. Ask for the qualified engineer instead, or move the appointment.

How do I check the certificate is genuine?

Take the certificate number and the awarding body name off the card, then contact that organisation using details you looked up yourself rather than a number printed on the card. Ask them to confirm the holder and the expiry. Competent person scheme operators also publish searchable registers, which is the quickest route when the engineer belongs to one.

Then do the half people skip. Confirm that the name on the card belongs to the person who will do the work. On a two person visit it is common and perfectly fine for one engineer to hold the certificate and the other to be an improver, as long as the certificate holder is the one commissioning the safety devices and signing the record. What you do not want is a card belonging to somebody who is at another address today.

If you booked through a call centre, a comparison platform or a trading name, ask which legal business you are contracting with as well. The certificate answers competence. It does not tell you who is liable if something goes wrong, and those are often two different companies. A firm working straightforwardly answers that in one sentence.

Does Gas Safe registration cover unvented cylinders?

No. Gas registration covers gas pipework and gas appliances, and unvented hot water is not gas work, so a Gas Safe search comes back clean for somebody who has never been assessed on a sealed cylinder. The two certificates are issued by different bodies, expire on different cycles and prove different things. Plenty of engineers hold both. Plenty hold one.

Our position is that if you only ask one question about a cylinder job, ask for the unvented certificate rather than the gas card, because it maps onto the parts being disturbed. That matters more in London than almost anywhere, since so much hot water here comes off an electric cylinder, a thermal store in a purpose built block or a heat pump cylinder, with no gas appliance in the system at all. Knowing how to check a plumber on the Gas Safe Register is still worth having, because the moment a gas appliance is heating that cylinder you need both answers rather than one.

What a qualified engineer does in the first ten minutes

Watch the order of operations, because it is the most honest signal available and no card is needed to read it. Somebody assessed on unvented systems looks at the safety chain before touching anything: incoming mains pressure and flow, the setting on the pressure reducing valve, the tundish and the route the discharge takes, both relief valves, and the data plate giving make, model and rated pressures.

The reason is that a sealed cylinder tells you most of what is wrong from the evidence around its valves before a spanner comes out. Scale on a tundish means it has discharged before. A discharge pipe reduced in bore, run uphill, or terminating where it would scald somebody is a fault with nothing to do with why you called, and a qualified engineer raises it anyway. Compare that with the visit that starts at the immersion heater because it looks like the answer.

• Reads the data plate for make, model, capacity and rated operating pressure.
• Checks incoming pressure and the pressure reducing valve setting rather than guessing them.
• Follows the discharge pipe from the tundish to where it terminates outside.
• Tests the expansion relief valve and the temperature and pressure relief valve, and confirms both reseat.
• Writes readings down as they go, instead of reconstructing them at the van afterwards.

Signs the person in front of you is not qualified for unvented work

The clearest early sign is language. Somebody who calls the tundish an overflow, uses safety valve for both relief valves without distinguishing them, or calls the cylinder a tank throughout, is telling you which world they normally work in. Vocabulary alone condemns nobody. Combined with reluctance to show a card, it is enough to stop the job before anything is opened.

The serious signs are proposals that remove protection: capping or plugging a discharge to stop it dripping, fitting a relief valve because it was the one on the van rather than because it matches the rating on the plate, taking a tundish out to tidy a cupboard, or reducing the bore of a discharge pipe to make a run fit. Each of those makes the visible problem go away and leaves the cylinder with one fewer layer between normal running and a failure nobody sees coming.

One more pattern worth naming: the engineer who will not test the relief valves in case testing makes them leak. That risk is real, old valves do sometimes fail to reseat afterwards, and it is still the wrong answer. A valve that will not reseat after a test was already a valve you could not rely on. Finding that out with a competent engineer standing there is the entire point of the exercise.

If the proposed repair is to stop a discharge rather than find out why the cylinder is discharging, get a second opinion from somebody holding the certificate.

What should the paperwork say after unvented work?

You should be handed a written record naming the engineer, quoting the certificate number, identifying the cylinder by make, model and serial number, listing the readings taken and the parts replaced with their ratings, and dated with the next service due. A record that says serviced cylinder, all in order, with a tick and a signature, is not a service record. It is a receipt.

The readings are what make the document worth keeping, because the next engineer reads them as a baseline. For a new installation there is a second document, since the work is notifiable, so you should also end up with notification confirmation and the manufacturer commissioning section of the manual filled in with real figures rather than a row of ticks. Keep both with the deeds paperwork, because a conveyancing solicitor asks for exactly this and reconstructing it years later from an invoice is unpleasant.

• Engineer name and unvented certificate number, not only a company stamp.
• Cylinder make, model, serial number and rated operating pressure.
• Incoming static and running pressure, and the pressure reducing valve setting left in place.
• Both relief valves tested, with whether each one reseated recorded honestly.
• Thermostat setting, thermal cut out checked, discharge pipe and termination checked.
• Parts fitted named with their ratings, and the date the next service falls due.

London blocks, conversions and new builds change the question slightly

In a purpose built block you may not have an unvented cylinder at all. Many blocks run thermal stores, including Pulsacoil type units, which store heated water and pass mains water through a heat exchanger rather than storing it under pressure. The unvented certificate is not the assessment that unit sits under, and an engineer who has never opened one will struggle whatever cards they hold, so ask whether they have worked on that model before.

In a Victorian conversion the cylinder has usually been changed more than once by different trades, with the discharge improvised to suit a route that did not exist when the building went up, and there is frequently no paperwork at all. An engineer who documents what is actually installed on the first visit is doing you a real favour. Hard water across the London supply area is the backdrop to all of it, since scale shortens component life and makes recorded readings worth more here.

What to do if unvented work has already been done by somebody unqualified

Get the system inspected by somebody who holds the certificate before assuming either the best or the worst. An inspection is not a big job. An engineer reads the cylinder plate, checks the safety components against what that cylinder requires, tests the relief valves, follows the discharge and tells you whether what is fitted is right for the appliance. That gives you a fact instead of an argument. Where the inspection does find something wrong, an unvented cylinder repair carried out by somebody holding the certificate also produces the record that was missing the first time.

Handle the paperwork separately. If you paid a business you are entitled to ask for the record and the certificate number of whoever attended, and a firm operating properly will send it. If a new installation was never notified, that gap surfaces at sale or remortgage, and your inspecting engineer can explain the route to regularise it. Keep the invoices and photograph the cylinder and its discharge in the meantime, because on a sealed system the history is half the diagnosis.