Glossary · Heat pumps, grants and regulations
What is Building Regulations Part L?
Part L of the Building Regulations is the part of the law in England that sets energy efficiency standards for buildings. Approved Document L explains how to meet it. For a boiler replacement it covers minimum efficiency, controls and commissioning, and the installer must give you a compliance certificate.
Key points
- Part L covers energy efficiency. For a replacement gas boiler, Approved Document L sets a minimum efficiency of 92% (ErP) in existing homes, with limited exceptions.
- When a boiler is replaced the controls should meet the standards too, and are treated as part of the boiler installation.
- New or replacement boilers are notifiable work. An installer on a competent person scheme can self-certify it and should issue a compliance certificate.
- If you do not receive the certificate within 30 days of completion, contact the installer's competent person scheme operator.
- A 2026 edition of Approved Document L takes effect on 24 March 2027 for most building work. The 2021 edition still applies until then.
How Part L works
Part L of Schedule 1 to the Building Regulations 2010 covers energy efficiency. Approved Document L is the statutory guidance that explains how to meet it in England.[2]Ministry of Housing, Communities and Local Government, Approved Document L: Energy and greenhouse gas emissions (2026) The guidance that applies today is the 2021 edition incorporating 2023 amendments. A new 2026 edition takes effect on 24 March 2027 for building work in England that is not connected with higher-risk buildings.[3]Ministry of Housing, Communities and Local Government, Approved Document L: Energy and greenhouse gas emissions, Volume 1: Dwellings (2026 edition)
Part L matters when you replace a boiler because GOV.UK lists installing or replacing a heating system, and adding extra radiators, among the alterations that may need building regulations approval. You do not need to get approval yourself if you use someone registered with a competent person scheme. You do not need advance approval for emergency repairs to a boiler, but there are rules to follow.[4]GOV.UK, Building regulations approval
What Part L asks for when a boiler is replaced
Approved Document L (2021) gives these points for an existing home.[1]Ministry of Housing, Communities and Local Government, Approved Document L, Conservation of fuel and power, Volume 1: Dwellings, 2021 edition incorporating 2023 amendments
| Topic | What the guidance says |
|---|---|
| Gas boiler efficiency | Minimum 92% (as defined in ErP) for wet heating such as radiators or underfloor heating. In exceptional circumstances, SEDBUK 2009 figures of 78% for natural gas or 80% for LPG are accepted |
| Combination boilers | At least one extra measure: flue gas heat recovery, weather compensation, load compensation or a smart thermostat with automation and optimisation |
| Controls | Boiler controls meet the standards and count as part of the boiler installation. A boiler interlock is fitted. Each room has thermostatic room controls, which can be a thermostat plus thermostatic radiator valves |
| Time control | Hot water and heating should each have separate time controls, unless a single controller already runs both |
| Flow temperature | A fully replaced wet system should be sized to work at a maximum flow temperature of 55°C or lower where feasible |
| Commissioning | Boiler and system commissioned to the manufacturer’s instructions. Circuits cleaned and flushed and an inhibitor added |
A separate section covers commissioning. A commissioning notice must be given to the building control body, within 30 days where the installer is registered with a competent person scheme, and the installer may give that notice.[1]Ministry of Housing, Communities and Local Government, Approved Document L, Conservation of fuel and power, Volume 1: Dwellings, 2021 edition incorporating 2023 amendments The guidance notes that the Benchmark commissioning checklist can be used to show that commissioning was carried out satisfactorily.[1]Ministry of Housing, Communities and Local Government, Approved Document L, Conservation of fuel and power, Volume 1: Dwellings, 2021 edition incorporating 2023 amendments
The compliance certificate for a boiler
New or replacement boilers are listed as notifiable work in the government leaflet for householders.[5]Ministry of Housing, Communities and Local Government, Building work, replacements and repairs to your home An installer on a competent person scheme can self-certify the work. The Gas Safe Register is one of the schemes on the GOV.UK list.[6]Ministry of Housing, Communities and Local Government, Competent person scheme - current schemes and how schemes are authorised Such an installer should notify the local authority and issue you a certificate of compliance, either directly or through the scheme operator. If you do not receive it within 30 days of completion, contact their scheme operator.[5]Ministry of Housing, Communities and Local Government, Building work, replacements and repairs to your home
If you do not use a registered installer, you would have to submit a building notice or full plans application and pay for a building control body to inspect the work.[5]Ministry of Housing, Communities and Local Government, Building work, replacements and repairs to your home Without approval you will not have the certificates of compliance you may need when you sell your home.[4]GOV.UK, Building regulations approval Anyone employed to work on gas appliances in a home must be a Gas Safe registered engineer, so check an engineer’s registration before work starts.[7]Health and Safety Executive, Domestic gas: frequently asked questions
Example
Dev in Leeds has his old regular boiler replaced with a new gas condensing combi. His installer is Gas Safe registered and on a competent person scheme. After the job Dev receives a handover pack that includes the completed commissioning record. Within a few weeks he also receives the Building Regulations compliance certificate. He files both so they are ready when he sells the house.
What people get wrong
People often think the Gas Safe check is the same thing as the Building Regulations certificate. They are different. Gas Safe registration shows the engineer is allowed to work on gas appliances. The compliance certificate shows the energy efficiency and controls standards were met and the work was notified.
The second mistake is thinking Part L only applies to new-build homes. It also covers replacement boilers in existing homes, which is why the controls and flow temperature rules in this page apply to ordinary boiler swaps. The 2021 guidance remains the current standard for most work until the 2026 edition takes effect.[3]Ministry of Housing, Communities and Local Government, Approved Document L: Energy and greenhouse gas emissions, Volume 1: Dwellings (2026 edition)
The bottom line
Part L is the energy efficiency part of the Building Regulations for England. When you replace a boiler it sets a minimum efficiency, standards for controls and a requirement to commission the system and notify the work. Use an installer on a competent person scheme and expect a compliance certificate within 30 days. Keep it safe for when you sell. See our boiler installation service for how BASI handles this.
Common questions
Do I need Building Regulations approval to replace a boiler?
Yes, in the sense that the work must be notified. Installing or replacing a heating system is covered. You do not need to apply yourself if the installer is registered with a competent person scheme, such as the Gas Safe Register for gas boilers.
What is a Building Regulations compliance certificate?
It is the certificate your installer or their scheme issues to confirm the work complies with the Building Regulations. You may be asked for it when you sell your home. It should arrive within 30 days of completion.
What happens if my installer is not on a competent person scheme?
You would have to submit a building notice or full plans application and pay a building control body to inspect the work. Work that does not comply is not legal and the local authority could require it to be put right at your expense.
What minimum efficiency must a new gas boiler meet?
Approved Document L's 2021 edition sets 92% (as defined in ErP) for wet heating in existing homes. In exceptional circumstances, using the Condensing Boiler Installation Assessment Procedure, lower SEDBUK 2009 figures of 78% for natural gas are accepted.
Sources
We cite the original source for every figure: government, regulators, standards bodies and manufacturers' own documents. Each one shows the date we last checked it.
- Ministry of Housing, Communities and Local Government. Approved Document L, Conservation of fuel and power, Volume 1: Dwellings, 2021 edition incorporating 2023 amendments. Checked 11 November 2026. ↩
- Ministry of Housing, Communities and Local Government. Approved Document L: Energy and greenhouse gas emissions (2026). Checked 11 November 2026. ↩
- Ministry of Housing, Communities and Local Government. Approved Document L: Energy and greenhouse gas emissions, Volume 1: Dwellings (2026 edition). Checked 11 November 2026. ↩
- GOV.UK. Building regulations approval. Checked 11 November 2026. ↩
- Ministry of Housing, Communities and Local Government. Building work, replacements and repairs to your home. Checked 11 November 2026. ↩
- Ministry of Housing, Communities and Local Government. Competent person scheme - current schemes and how schemes are authorised. Checked 11 November 2026. ↩
- Health and Safety Executive. Domestic gas: frequently asked questions. Checked 11 November 2026. ↩