The certificate for an unvented hot water cylinder is a Building Regulations compliance certificate for the installation, often called a G3 certificate. In England it comes from an installer registered with a competent person scheme, who notifies the work so it is recorded with the local authority. It is issued once, for that installation. A yearly service does not renew it, and a gas safety record is a separate document with a separate purpose. This page sets out what the certificate covers, who may issue it, and the route open to you when no certificate was ever handed over.
Is a certificate required for an unvented hot water cylinder in England?
Fitting an unvented hot water cylinder in England is building work, so it has to be signed off under the Building Regulations 2010. Part G3 of Schedule 1 sets the standard the installation must meet. Stored water must never exceed 100 degrees Celsius, and any discharge from a safety device must be visible but go somewhere safe. The same part requires the system to withstand temperature and pressure in normal use and in reasonably anticipated malfunctions, and to be adequately supported.
Regulation 12 of those regulations requires building work to be notified by building notice or full plans application. The exception is work listed in column 1 of the table in Schedule 3, carried out by a person named in column 2. Installation of a heating or hot water system, or associated controls, sits on that Schedule 3 list. The document you should end up with is the Building Regulations compliance certificate for the installation.
The compliance certificate belongs with the house, not with the person who paid for the work. GOV.UK guidance notes that these records are asked for when a home is sold, so keep it with the property paperwork.
Who can issue the Building Regulations certificate for an unvented cylinder?
An installer registered with a competent person scheme issues the certificate for an unvented cylinder, either directly or through the scheme operator. Approved Document G, the official guidance to Part G for use in England, accepts competence shown by membership of such a scheme. A valid registered operative card for unvented hot water systems is the other route it names.
Where the installer is not registered with a scheme, the building control body has to be notified before the cylinder is installed. The certificate therefore depends on who does the work, and on that notification being made at the right time. A general plumber without unvented registration cannot self-certify the job. Our guide on who can install an unvented hot water cylinder goes through the qualifications in more detail.
G3 compliance certificate or Benchmark commissioning record: which document is which?
Two different documents arrive with a new unvented hot water cylinder, and people often mix them up. The Building Regulations compliance certificate records that the installation was notified and complies in England; the Benchmark record shows the unit was commissioned and keeps the manufacturer warranty conditions satisfied.
| Criterion | Building Regulations compliance certificate | Benchmark commissioning record |
|---|---|---|
| What it shows | The installation was notified and meets the Building Regulations 2010, Part G3, in England | The cylinder was commissioned and set up to the manufacturer instructions |
| Who completes it | Installer registered with a competent person scheme, or the scheme operator on their behalf | The competent installer fills in and signs it; the customer countersigns |
| Where it ends up | Sent to you and the work recorded with the local authority | Left with the householder as part of the appliance paperwork |
| Kept up to date | Issued once for that installation, not reissued each year | Service record section continued at every service visit |
| Why it matters later | Asked for by a buyer solicitor when the home is sold | Manufacturer warranty terms rely on proof of yearly servicing |
No certificate arrived after the unvented cylinder was fitted: what can you do?
Contact the installer competent person scheme operator if no compliance certificate reaches you within 30 days of the work being completed. GOV.UK guidance for homeowners sets out exactly that step. The scheme operator holds the registration and the notification record for the installer who did the job.
Where the work was never notified at all, Regulation 18 of the Building Regulations 2010 gives the owner a route. You can apply in writing to the local authority for a regularisation certificate, for unauthorised work carried out on or after 11 November 1985. The application needs a description of the work and, so far as is reasonable, a plan of it.
The authority may require parts of the work to be opened up for inspection, tests to be carried out and samples to be taken. A regularisation certificate counts as evidence of compliance, but not as conclusive evidence. Nobody can promise in advance that one will be granted, so treat it as an application rather than a formality.
What the installation behind an unvented cylinder certificate has to include
An unvented hot water storage system is fed directly from the mains and has no open vent pipe to the atmosphere. Approved Document G expects at least two independent safety devices guarding against overheating and overpressure. These are a non-self-resetting energy cut-out plus a temperature relief valve, or a combined temperature and pressure relief valve. Systems up to 500 litres and under 45 kW should be installed as a proprietary unit or package that has been tested as a whole.
Everything in that list is work for a suitably qualified engineer, not for a householder. Relief valves, the expansion vessel, the tundish and the discharge pipework must not be adjusted or tested by the person living in the home. Safe checks at home are limited to boiler pressure, thermostat and programmer settings, the reset button and bleeding radiators. If you are planning a cylinder or replacing an old one, see Megaflo and unvented systems for how we survey and quote the work.
Does the annual service produce a new unvented cylinder certificate?
No. The Building Regulations compliance certificate covers the installation once, and a service visit adds an entry to the service record instead. Worcester Bosch cylinder instructions state that the Benchmark commissioning checklist must be completed and left with the householder, and that the service record is continued at each service. The same instructions tie an annual service to safety and to keeping the warranty in force.
Heatrae Sadia says the strainer, pressure reducing cartridge and expansion valve cartridge on a Megaflo Eco may need checking and cleaning yearly, depending on water quality. Its manual puts that work with a competent person, often at the same visit as the boiler service. Our guide on servicing unvented cylinders and Megaflo systems explains what the visit covers.
A gas safety record is not an unvented hot water cylinder certificate
A gas safety record and an unvented cylinder compliance certificate prove different things. The gas safety record relates to gas appliances, pipework and flues under the Gas Safety (Installation and Use) Regulations 1998 as amended, and that work belongs to a Gas Safe registered engineer. It says nothing about whether the cylinder installation met Part G3 in England.
Where a gas boiler heats the cylinder, a household can hold both documents for the same system. One covers the gas appliance and its safety; the other covers the building work that put the cylinder in. A buyer solicitor asking for cylinder paperwork will not be satisfied by a gas safety record alone.
If your cylinder is due its yearly check and you want it looked at alongside the boiler, you can arrange a visit through boiler service and repairs.
Sources
- Building Regulations 2010, Schedule 1 (Part G3, hot water supply and systems)
- Building Regulations 2010, Regulation 12 (giving a building notice or depositing full plans)
- Building Regulations 2010, Schedule 3 (self-certification schemes and exemptions)
- Building Regulations 2010, Regulation 18 (regularisation certificate)
- GOV.UK — Building work, replacements and repairs to your home
- Approved Document G: sanitation, hot water safety and water efficiency (with 2024 amendments)
- Worcester Bosch — cylinder installation and maintenance instructions
- Heatrae Sadia — Megaflo Eco installation manual
- HSE — legislation interfacing with the Gas Safety (Installation and Use) Regulations 1998