Our programme of research delivers a major portfolio of reports and practical guides

At your services: what to expect during commissioning (NF84)

Site managers rely heavily on commissioning to ensure their new-build homes perform successfully. However, the process of commissioning of services has become an area of considerable specialism, supported by its own professional bodies. Commissioning is often a legal requirement and for reasons of safety quite rightly a task that should only be undertaken by suitably qualified people.

In practice, this increased specialism has led to site managers becoming more distant from the services-commissioning activities that are pivotal to the successful operation of the homes they build.

Investigations by the NHBC Foundation and others, highlight that commissioning may not always be identifying the adjustments and deficiencies that it is designed to detect.

This practical, illustrated guide, developed collaboratively with BSRIA, introduces the commissioning of domestic services and aims to give site managers sufficient insight to be inquisitive about the commissioning activities that they should expect to see on their sites.

Summary of content


  • This illustrated guide for site managers is a practical checklist with simple explanations for the non-expert. It highlights the diversity and complexity of modern domestic services.
  • It identifies that the correct sequencing of commissioning works is vital to avoid costly delays or remedial actions.
  • It identifies the important compliance documents and labelling required for commissioning; produced by expert installers and technicians who record details of checks and tests.
  • The guide is not intended to give you detailed guidance on commissioning procedures themselves, but a summary of what you should see taking place and important documents you should be asking for.

Services included in the guide are:

Water and drainage installations – to avoid serious damage to homes from leaks, the Water Regulations require hot and cold water pipes to be flushed and pressure tested, and the Building Regulations require watertightness testing for all drains.

Gas connection and distribution pipes – tests are carried out to ensure the gas installation is safe.

Electrical installations – by law, the electrical installation in a home must be tested to check that it is safe. Any faults can result in electrical fires and electric shocks.

Boiler – gas supply and correct operation – commissioning ensures that boilers (and other gas appliances) are operating safely. All tests must be carried out by a gas engineer who is on the Gas Safe Register.

Conventional central heating circuits with radiatorsthe aim is to ensure that the heating circuit does not leak, is protected from internal corrosion and is set up to work efficiently.

Underfloor heating pipe loops and manifoldscommissioning places particular focus on avoiding any damage and consequential leaks from the pipe loops, as repairs are very costly and hugely disruptive.

Unvented, indirect hot water cylinders because unvented hot water cylinders store and distribute hot water under pressure, correct commissioning is important for safe operation.

Ventilation systemsproper testing and commissioning is needed to ensure correctly-operating ventilation systems that deliver good indoor air quality and minimise the risk of mould and condensation. All mechanical ventilation systems must be tested for the airflow they deliver.

Air source (air-to-water) heat pumpsThe heat pump and its integration with the home’s heating system (and often the hot water cylinder) requires specialist commissioning to ensure efficient operation. This guide only covers packaged (also known as monobloc) air-to-water heat pumps, the most common type encountered.

Solar hot water systems solar hot water systems should only be installed and commissioned by those who are competent do so. This guidance provides generic steps for the commissioning of a typical (indirect) system.

Grid-connected photovoltaic (PV) systemsPV systems must be commissioned correctly in order to work safely and efficiently and to have a long life.

Final checks on completion

A round of final checks is recommended once the home is complete. Some quick and easy final checks are listed.