What is Boiler Commissioning?

James Elston
Written by James Elston
Updated on 19th March 2024
Posted on 1st March 2024
Topic: Boiler Advice
boiler commissioning

Boiler commissioning is more than a formality—it’s essential for the safety and efficiency of your new heating system.

inside boiler

It’s a vital legal requirement in the UK for any new boiler installation. This article offers a clear overview of the commissioning process, detailing the necessary steps and outcomes you should expect without delving into overly technical jargon.

Here, you’ll learn about the pivotal role of a Gas Safe registered engineer and how proper commissioning can save you money and ensure long-term system reliability.

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Commissioning a Boiler Overview

  • Boiler commissioning is a mandatory legal requirement for new boiler installations in the UK, carried out by a qualified Gas Safe registered engineer to ensure safety standards and energy efficiency are met.
  • The comprehensive boiler commissioning process includes pre-commissioning checks, verification of connections, water and fuel system checks, safety and performance tests, concluding with system cleansing, and guarantee registration.
  • Homeowners have a vital role in the commissioning process by choosing the right boiler and engineer, understanding the manufacturer’s instructions and warranty, and maintaining proper servicing to ensure the longevity and safety of their heating system.

What is Boiler Commissioning?

The process of boiler commissioning plays a vital role in new boiler installations. It guarantees optimal setup of the system for sufficient heat and hot water, while also minimising energy usage.

By law, this process must be performed by a qualified Gas Safe registered engineer, ensuring safety standards are met and the commercial boiler system operates at peak efficiency.

Boilers installed in the UK since April 2018 are required to achieve a minimum energy efficiency of 92% and have functioning timers and temperature controls. This regulation aims to improve energy efficiency and reduce environmental impact.

This requirement is not just an environmental initiative, but a legal mandate. The successful completion of the boiler commissioning process is certified by a building regulations compliance certificate, a mandatory legal document that serves as proof of the boiler’s safe installation.

Therefore, boiler commissioning goes beyond being just a recommendation; it’s a mandatory legal requirement for all new boiler installations.

The Role of a Gas Safe Registered Engineer

A Gas Safe registered engineer is the principal actor in the boiler commissioning process. But who are these professionals, and why are they so important in this procedure?

To begin with, Gas Safe registered heating engineers have the required training and accreditation to work safely with gas heating systems. They are equipped to handle the complexities of a new boiler installation, ensuring proper installations and repairs.

Engaging a Gas Safe registered engineer goes beyond merely completing the job; it’s a matter of ensuring safety. The risks associated with gas leaks, fire, boiler explosion, or carbon monoxide poisoning due to poorly fitted or maintained gas appliances are severe.

A Gas Safe registration assures you that the engineers are up-to-date with modern systems, materials, and legislation, safeguarding your home from potential safety issues post-installation.

Our Expert Gas Safe Engineer Says:

The commissioning of a boiler is what every expert Gas Safe registered heating engineer should do. This is important and is the final check to show that your boiler has been installed correctly.

James Murfin

Gas Safe Registered Heating Engineer

Benefits of proper boiler commissioning

Proper boiler commissioning is not only a regulatory requirement but also a key factor in achieving long-term benefits. One such advantage is the validation of the manufacturer’s warranty for a new boiler, which requires proof of proper installation and commissioning by a qualified engineer.

Additionally, proper commissioning optimises boiler performance, potentially reducing the risk of future costly boiler repairs and extending the lifespan of the system.

It’s a process that encompasses performance tests to verify a boiler’s efficiency, combustion quality, and emission levels. The boiler output is also adjusted during commissioning, important for maintaining system efficiency and reducing energy costs.

Hence, investing in proper boiler commissioning yields long-term benefits by guaranteeing the peak performance of your central heating system.

Boiler Commissioning Process: Step-by-Step Guide

The boiler commissioning process, also known as the boiler commissioning procedure, follows a series of meticulous steps to ensure your heating system’s safety and efficiency. With a boiler commissioning checklist provided, these steps include:

  1. Pre-commissioning checks and initial inspection
  2. Verification of mechanical and electrical connections
  3. Water and fuel system checks
  4. Safety and functional tests
  5. Performance evaluations

Let’s examine each step in detail to understand their implications.

Pre-commissioning checks and initial inspection

Before the actual commissioning process begins, pre-commissioning checks and an initial inspection are conducted.

These checks are essential to ensure that the boiler installation adheres to all relevant regulations, standards, and manufacturer guidelines.

The initial inspection aims to confirm that the boiler is undamaged, with no leaks or loose connections after transportation and installation.

It’s a vital step that sets the stage for the subsequent phases of the commissioning process. It’s like the pre-flight checks a pilot performs before takeoff, ensuring everything is in order for a safe and smooth flight.

Mechanical and electrical connections

Ensuring the correct installation and accurate connection of mechanical components forms a critical step in the commissioning process. This includes components like:

  • pumps
  • fans
  • valves
  • controls

It also includes electrical connections and pressure-relief settings.

During this process, the following steps are taken to ensure the proper installation and functioning of your heating system:

  1. Test connections are implemented to facilitate thorough commissioning tests.
  2. The boiler’s insulation is checked and maintained to prevent heat loss and uphold the heating system’s efficiency.
  3. Expansion mechanisms are installed and verified to accommodate thermal expansion of the boiler during operation.

This meticulous scrutiny ensures that your heating system is set up correctly, leading to maximum efficiency and problem-free operation.

Water, fuel system, and gas supply check

The next step in the commissioning process is checking the water, fuel system, and gas supply. This involves carrying out a gas tightness test to verify that the gas pressure in the property’s gas supply pipe is maintained and prevent potential gas leaks.

Furthermore, during a boiler inspection, the following checks are performed:

  • The gas rating of the boiler is checked to ensure that it is connected to a properly sized pipe and that the system runs smoothly.
  • The boiler is checked for any blockages that may be causing issues.
  • These checks ensure that your boiler operates safely and efficiently, providing you with reliable heating when you need it most.

Safety and functional tests

The commissioning process considers safety and functional tests as integral components. The Gas Safe engineer conducts these tests to verify the proper operation of the boiler, including:

  • Testing the ignition system
  • Testing burner operation
  • Testing gas working and standing pressure
  • Testing other specific boiler features

Pressure tests confirm the boiler’s ability to handle expected operating pressures without leaks or failures.

Safety interlock tests check the function of the boiler’s safety mechanisms, which prevent operation under unsafe conditions, while testing safety controls, alarms, and shutdown mechanisms ensure they respond correctly to hazards and can shut down the system safely if needed.

These tests are not just about ticking boxes; they’re about ensuring your safety and the optimum performance of your heating system.

Performance and efficiency evaluation

Performance and efficiency evaluation marks the concluding phase of the commissioning process. This involves conducting performance tests such as flue gas analysis to ensure the boiler is burning gas correctly, which is imperative for its efficiency, combustion quality, and emissions.

The boiler’s output is adjusted according to the size of the property and the number of radiators, ensuring energy-efficient operation and preventing unnecessary energy waste.

This fine-tuning is an essential part of the performance evaluation, ensuring the system’s overall efficiency. After all, what’s the point of having a high-performing boiler if it’s not optimally adjusted to meet your specific heating needs?

Boiler Commissioning Checklist: Essential Steps for Engineers

Once the commissioning process is complete, the Gas Safe engineer follows a boiler commissioning checklist. This checklist, provided by the Hot Water Council, serves as a comprehensive guide to ensure nothing is overlooked. It includes:

  • System cleansing
  • Corrosion inhibitor application
  • Gas flue analyser test
  • Gas rate measurement
  • Boiler output adjustment
  • Gas tightness test
  • Registration of the boiler guarantee

Let’s further investigate these steps.

System cleansing and corrosion inhibitor application

System cleansing is an important part of the commissioning process. This step involves:

  • Flushing the new system according to the manufacturer’s instructions
  • Removing debris and flux
  • Ensuring nothing harmful remains that could compromise the new boiler.

A corrosion inhibitor is then added to the system to help protect radiators, prevent hydrogen gas formation, and enhance both the efficiency and longevity of the boiler.

This process is checked to ascertain its distribution throughout the system and guard against corrosion.

In essence, system cleansing and corrosion inhibitor application are akin to preparing a clean and safe environment for your new boiler to operate in.

Gas flue analyser test and gas rate measurement

Following on the checklist are the flue gas analyser test and gas rate measurement. The boiler flue gas analyser test is mandatory to ensure the boiler is burning the gas correctly and safely.

Measurements of flue gases are taken and must be recorded in the benchmark book accompanying the new boiler installation to certify that gases are within safe and optimal levels.

In addition, the gas rate measurement verifies that the gas pressure and rate are within the boiler’s specifications and comply with legal requirements.

This process is so important, particularly when connected to new pipework, to ensure proper fitting and unobstructed operation.

Boiler output adjustment and guarantee registration

The boiler’s output settings must be adjusted according to the size of the house and the number of radiators to ensure energy efficiency. This is an essential step in the commissioning process, ensuring the boiler delivers optimal heat output without wasting energy.

Finally, registering the boiler’s guarantee is an essential step for warranty purposes, providing homeowners with long-term coverage and peace of mind.

The engineer is responsible for registering the boiler’s guarantee through installer apps and should explain the guarantee details and operational procedures to the homeowner upon completion of commissioning.

Can I use a boiler that is not commissioned?

If a boiler is not commissioned, then you should not use it.

As the process ensures the boiler operates safely and efficiently, and while not a legal requirement, it serves as evidence of proper installation and is important for warranty purposes. Therefore, your boiler may not be safe, plus if anything goes wrong, the boiler warranty will be invalid.

Tips for Homeowners During Boiler Commissioning

While boiler commissioning may seem like a process only for engineers, homeowners play a key role too. From selecting the right boiler and engineer to understanding the manufacturer’s instructions and warranty details and maintaining proper servicing, homeowners’ involvement is key.

After all, understanding your heating system will empower you to manage it efficiently and know whom to contact for support or service.

Wondering how homeowners can stay informed and involved during the commissioning process? Here are some top tips for homeowners to consider during boiler commissioning.

Selecting the right boiler and engineer

The initial step towards a successful commissioning process lies in choosing the right boiler and engineer. The right boiler type, such as conventional, combi, or system boilers, should be selected by considering the size of your property and hot water needs.

Additionally, the appropriate fuel type, which can include mains gas, oil, or renewable energy like biomass, should be chosen.

It is also pivotal to hire a Gas Safe registered engineer for the safe and competent installation of the boiler. Remember, the right choices at this stage can set the foundation for an efficient and safe heating system.

Understanding manufacturer’s instructions and warranty details

For homeowners, it is of utmost importance to understand the manufacturer’s instructions and warranty details. Registering the boiler guarantee is vital for receiving technical support from the manufacturer and ensuring warranty protection.

Warranty documents detail the specific components covered, such as:

  • the flue
  • the pump
  • the heat exchanger
  • the control PCB

These warranties provide repairs or replacements for faults occurring within the warranty period.

Beyond manufacturer’s warranties, the Consumer Rights Act of 2015 offers the right to a free repair or replacement within a certain time after purchase in case of failure.

Therefore, understanding and complying with warranty terms and conditions is mandatory.

Proper maintenance and servicing

Regular maintenance and servicing of your boiler can provide several benefits, including:

  • Extending boiler lifespan
  • Ensuring safety
  • Avoiding expensive repairs
  • Extending warranty periods
  • Ensuring continued effectiveness

From maintaining the correct water pressure for optimal heating circulation to bleeding radiators to release trapped air, homeowners have a pivotal role in maintaining their heating systems.

Moreover, activating the heating system monthly allows homeowners to check for and prevent the development of potential problems.

Early detection of issues, such as leaks or unusual noises, is key for prompt repairs and maintaining safety.


We’ve journeyed through the intricate process of boiler commissioning, dissecting its various steps, understanding the role of a Gas Safe registered engineer, and appreciating the benefits of proper commissioning.

Boiler commissioning isn’t just a technical process; it’s a commitment to safety, efficiency, and long-term savings.

As homeowners, understanding this process is imperative. It empowers you to make informed decisions, from selecting the right boiler and engineer to performing regular maintenance. Remember, an efficient heating system isn’t just about comfort on cold winter nights; it’s about safety, sustainability, and peace of mind.

Frequently Asked Questions

How long does it take to commission a boiler?

Commissioning a boiler usually takes a few hours to a full day, but it may vary based on the boiler’s specifications.

What are the consequences of not commissioning a central heating system?

Not commissioning a central heating system can lead to consequences such as excessive energy consumption, excess boiler noise, and general system wear and tear. It’s important to prioritise proper commissioning to avoid these issues.

How do I get a gas commissioning certificate?

To obtain a gas commissioning certificate, you can contact a Gas Safe registered engineer, who will notify the Gas Safe Register for you. Following this, your Building Regulations Compliance Certificate will be delivered to you by your local authority in 10-15 working days.

What does commissioning of a boiler mean?

Commissioning of a boiler involves checking the installation and setup to ensure maximum efficiency and to avoid common issues with the heating and hot water products. This includes confirming specific details about the work and informing the customer.

What does a Gas Safe registered engineer do?

A Gas Safe registered engineer is qualified to install and repair gas heating systems safely. They also perform the boiler commissioning process to ensure safe and efficient operation.

Written by
James Elston
James Elston Director Of Boiler Central
Posted on: 1st March 2024
Topic: Boiler Advice

James Elston is our resident boiler replacement and heating expert here at Boiler Central. With over 20 years experience in the boiler installation industry, James ensures that he knows everything there is about our Gas Safe boiler installations, energy saving and home heating solutions. This can be from simply procuring the latest best combi boilers, to reviewing and ensuring that Boiler Central maintains the highest standards across our boiler installation company.

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