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Who can install an unvented cylinder?

In this article we aim to answer the following questions:

  1. Do I need to be qualified to fit an unvented cylinder?
  2. Does my pressurised cylinder need commissioning?
  3. What does hot water cylinder commissioning involve?
  4. What are the rules for notifying the installation of an unvented hot water cylinder?


Do I need to be qualified to fit an unvented cylinder?

The simple and correct answer is YES.

Use a qualifed and certificated engineer.

As covered in a previous article, unvented and indeed vented cylinders can turn in to explosive devices, when not installed correctly and safety devices fail.

In the UK a qualification which covers Building Regulation G3 has to be taken EVERY 5 YEARS. So it expires.

Don’t assume that all plumbers, heating or gas engineers, or whatever they want to call themselves today, have one. Most in fact do not.

Ask to see their certificate. It should look similar to the below;

    an image showing an unvented hot water certificate

    Does my pressurised cylinder need commissioning?

    Yes it does.

    Commissioning is the immediate process that follows the installation of the pressurised cylinder.

    Like installing the cylinder, commissioning is for the professional and qualified engineer and should not be attempted by DIY-ers!

    Commissioning ensures the hot water cylinder is safe and ready for use.

    What does hot water cylinder commissioning involve?

    There are a few variations to the below, depending on whether you have a vented or an unvented cylinder. It will also depend whether your chosen cylinder has additional features, like the Mixergy cylinder for example.

    In general, the process involves purging and filling the cylinder before flushing, making sure the heat source (gas/oil boiler etc) is working as it should and that water is stored at the correct temperature, checking all the safety valves, pipework and discharge pipework are leak free and comply with the guidance as set out by building regulations G3.

    The next important step is to ensure the benchmark certificate (or logbook) is completed in full and correctly. This forms part of your guarantee and if not filled out your unvented hot water cylinder guarantee will be invalid. If you need to call upon the guarantee, the manufacturer will check everything has been installed correctly, the benchmark certificate has been completed, that a qualified engineer has fitted the cylinder and that all of the annual services have been carried out.

    What are the rules for notifying the installation of an unvented hot water cylinder?

    This is all about compliance with the Building Regs. Unvented hot water cylinder installations need to be notified to the Local Authority Building Control (LABC). This should be done by the installer either directly to the LABC or through a Competent Persons Scheme.

    A Building Regulations Compliance Certificate will then be issued to the householder. This includes a Notification Number for the householder to add to the Benchmark Commissioning Checklist. You will need to produce this if or when you sell your house, or in the event of an insurance claim. So keep it safe!

    Oh and finally…..

    It is vital that you do not ignore the notification.

    If hot water cylinder installation is not carried out correctly by a suitably trained installer, who is a member of a CPS, or is not checked by Building Control, your customers could be open to fines of up to £5,000.


    I hope you have found this article useful.

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