Skip to the entry
Boiler Look-Up
Subjects

Look-up › Replacing and paying

Building rules for a new boiler

Checked against its sources: Updated

Boiler building regulations differ by country: England applies Approved Document L's 2021 edition and Wales its 2022 edition, both with a 92% ErP minimum for gas boilers.12 Scotland and Northern Ireland have their own documents.34

Covers
England, Wales, Scotland and Northern Ireland, separately. Isle of Man building rules were not researched.
You
Keep the certificate, and ask which edition the quote works to.
A professional
Meeting the rules is the installer's job; registered competent persons self-certify. Gas Safe registered on gas.

1 By country

Minimum gas boiler efficiency in existing homes
CountryDocumentMinimum
EnglandAD L Vol 1, 2021 with 2023 amendments, Table 6.292% ErP; exceptional circumstances 78% SEDBUK 2009 natural gas, 80% LPG1
WalesAD L Vol 1, 2022, in effect since 23 November 202292% ErP2
ScotlandDomestic Building Services Compliance Guide 2022, consultation copy; final status not confirmed92% ErP3
Northern IrelandTechnical Booklet F1, June 2022, paras 3.32-3.3388% SEDBUK 2009 or 90% SEDBUK 2005; a replacement also not more than 2 points below the old boiler, whichever is greater4

2 England in detail

These are from the 2021 edition, and Wales has parallel combi, controls and hard water wording in its 2022 edition12.

England's main expectations when a boiler is replaced
TopicParagraphExpectation
Combi measure6.2One of four: recovering heat from flue gases, weather or load compensation, or a smart thermostat that automates and optimises1
Room controls5.20-5.22Thermostatic control in each room unless unheated or not feasible, with no TRV in the room that holds the thermostat1
Pipes4.25Insulate accessible pipes1
Commissioning8.8Clean and flush, add inhibitor, treat hard water, commission to BS 75931
Notice8.5A competent person sends it within 30 days of completion1
CO alarmAD J 3.43In the room with a new or replacement fixed gas appliance, except gas appliances used solely for cooking6

The name "Boiler Plus" does not appear in the text read. More on the room rule is under room thermostat, and on feed water under hard water treatment.

Installing a heating system may need approval, but a registered competent person can self-certify7. GOV.UK says Gas Safe is "not technically" such a scheme, yet in practice its installers have the same responsibilities8. Formal approval aside, GOV.UK says safety and energy efficiency standards must still be met9.

3 55°C and 60°C

Paragraph 5.10 of the 2021 edition applies where a wet system is newly installed or fully replaced, including appliance, emitters and pipework, and asks for "a maximum flow temperature of 55°C or lower"1. As worded, it does not reach a boiler swap on existing radiators. The 2026 edition reads "a maximum flow temperature of 55°C"5.

The 60°C figure is something else: running advice from the government's Clean Energy campaign for combi boilers10. See flow temperature.

4 What changes in 2027

England's 2026 edition takes effect on 24 March 2027, or 24 September 2027 for higher-risk work, and the Welsh one on 4 March 202752. In England's text the 92% figure stays, and a replacement must not fall below the one it replaces for the same fuel (para 4.5)5. A note under para 4.9 says that when only the appliance is replaced a whole dwelling heat loss calculation is appropriate, and that sizing from the old appliance's output "is not appropriate"5. That is not current law until the edition takes effect. Transitional detail for existing homes was not confirmed.

Sources

  1. Approved Document L for England, Volume 1, in-force 2021 edition with 2023 amendments read 3 November 2026; landing page.
  2. Part L guidance, Welsh Government and 2026 Welsh edition read 3 November 2026.
  3. Building standards collection, Scottish Government and 2022 compliance guide, consultation copy read 3 November 2026.
  4. Technical Booklet F1, June 2022, Department of Finance NI read 3 November 2026.
  5. New England edition, Approved Document L Volume 1, 2026 read 3 November 2026.
  6. Approved Document J, England, 2022 amendments, CO alarm guidance read 3 November 2026.
  7. When building approval is needed, GOV.UK read 3 November 2026.
  8. Current competent person schemes, GOV.UK read 3 November 2026.
  9. When you do not need approval, GOV.UK read 3 November 2026.
  10. Clean Energy campaign, GOV.UK, save energy in your home read 3 November 2026.