A circular like this one exists to tidy a document after it's published. Circular 04/2026 was published on 8 September 2026, and it corrected minor errors in the 2026 editions of Approved Documents L and F.

None of those corrections touches the rules for a replacement boiler. The efficiency minimums, the extra measures required of a gas combi and the heating controls your quote should name are the same as they were before the circular went out.

When the 2026 rules start

The 2026 edition of Approved Document L still takes effect on 24 March 2027. Until then, the earlier edition is what governs a boiler replacement, and the dates that decide which edition applies to a given job are set out in Circular 01/2026, not in this one.

If you want to check which edition your own installation falls under, work out which edition applies to your job against those dates. For what changes once the 2026 edition does apply, see what changed in the 2026 edition.

When the government publishes a new edition of an Approved Document, an older edition usually keeps applying to work that was already under way before the change took effect. That is called a transitional provision, and it turns "which edition applies to my job" into a question about dates: when the job started, when the contract was agreed, sometimes when the work is due to finish.

The dates that govern the 2026 edition

Circular 01/2026 sets out the transitional arrangements for the 2026 changes. The 2026 editions take effect on 24 March 2027, or 24 September 2027 for higher-risk building work. Until that date, a job that started under the previous edition stays under it, even once the 2026 edition is published.

Why getting this right changes the rest of the quote

An installer's quote that names an edition is only useful if that edition is the right one for your job's dates. Get the edition wrong and every figure and paragraph you check the quote against is wrong too.

You can check which edition applies to your own job against its dates, and see what changed between the 2021/2023 edition and the 2026 one.