How to Check Your Cylinder Installer Is G3 Qualified

Gas Safe registration and G3 are two different things

This is the single most common misunderstanding in cylinder work. Gas Safe registration covers work on gas appliances and gas pipework. Unvented hot water storage is a separate competence with its own qualification, usually referred to as G3 after requirement G3 of the Building Regulations, which covers hot water supply and systems. An engineer can hold one without the other. A perfectly legitimate Gas Safe registered boiler installer may have no qualification to touch an unvented cylinder, and a G3 qualified plumber may do no gas work at all.

That matters because unvented hot water work is notifiable building work. Someone has to certify it, and only someone qualified can.

Ask these before you book, not after

• “Who on your team holds the unvented hot water qualification, and will they be the person doing the work?” A firm may hold the competence collectively while sending someone who does not. Ask about the individual attending.
• “Which competent person scheme will notify this job?” A qualified installer registered with a competent person scheme can self-certify the work and have the Building Regulations compliance certificate issued to you. If they are not registered with one, the alternative is a building notice to your local authority building control before the work starts — which is legitimate, but it needs to be arranged, and it has a fee.
• “Can I see the certificate?” The qualification is evidenced by a certificate with a name and an expiry or renewal date on it. Asking to see it is normal and a qualified engineer will not be offended.

Verify rather than take it on trust

Two checks are worth doing yourself. First, look the business up on the register of whichever competent person scheme they name — the schemes publish searchable registers, and the listing shows what categories of work the registration actually covers, which is the part people skip. Second, check that the name on the qualification certificate matches the person turning up. A photograph of a certificate belonging to a former employee is not a qualification.

If someone will not name a scheme, will not show a certificate, or tells you the job does not need notifying because it is only a swap, treat all three as the same answer. Replacing an unvented cylinder is notifiable work regardless of whether one was there before.

The certificate is the thing you are actually buying

After the work, you should receive a Building Regulations compliance certificate for the unvented installation, alongside the manufacturer’s commissioning paperwork or Benchmark record. Keep both. That certificate is what a conveyancing solicitor asks for when you sell, what a manufacturer looks for if you claim on the cylinder warranty, and what an insurer may ask about after a water escape. An uncertificated unvented cylinder is not just a paperwork gap — it is a discount someone will ask for at the point of sale, and often a retrospective regularisation cost.

What a properly done job leaves behind

Beyond the certificate, a qualified installation is visible. The tundish should be somewhere you can actually see it, so that a discharging safety valve is noticed rather than hidden. The discharge pipe should run to a place where very hot water cannot scald anyone. The expansion vessel, pressure control and relief valves should be accessible for servicing rather than buried behind a boarded panel. And you should be told when the first annual service is due, because unvented cylinders are serviced to keep the safety devices proven and, usually, to keep the warranty valid.

The same check applies to a combined job

If the boiler and cylinder are being replaced together, both competences are needed — Gas Safe for the boiler, the unvented qualification for the cylinder — and both halves have to be notified, sometimes under a single scheme registration that covers both and sometimes under two. Ask how each half is being certified. Our cylinder replacement and combined boiler and cylinder surveys set out which scheme covers which part of the job before anything is booked, and the wider checklist in choosing a boiler installer applies here too.