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Words on a boiler quote
Checked against its sources: Updated
A boiler quote usually mixes rule terms, such as ErP efficiency and commissioning to BS 7593, with extras such as a filter or flush, and each can be checked against its source.12 Prices are not given here because no official figures exist.
- Covers
- Rule terms are from England's Approved Document L, 2021 edition with 2023 amendments. Other countries differ.
- You
- Ask what each line does and which rule, if any, needs it.
- A professional
- Choosing, fitting and commissioning all of it.
1 Rule terms
| Word on the quote | What it means |
|---|---|
| ErP 92% | The minimum efficiency for gas wet heating in an existing home, set in Table 6.21 |
| SEDBUK 2009 | A different efficiency rating, used for the exceptional-circumstance minimums: 78% natural gas, 80% LPG1 |
| Weather compensation | "A system which enables the operating flow temperature of a heating system to be varied", using an external sensor1 |
| Load compensation | A control that varies flow temperature against the heating system's measured response1 |
| Flue gas heat recovery | One of the four combi measures in para 6.2, alongside the two above and a smart thermostat with automation and optimisation1 |
| Boiler interlock | A control arrangement expected on boiler systems, so the system switches off with no demand1 |
| Thermostatic room controls | Room thermostat plus TRVs elsewhere, room or zone thermostats, or networked emitter controls1 |
| BS 7593 | The code of practice for preparing and commissioning the system1 |
| Benchmark | A checklist that "can be used" to show commissioning was done1 |
| Hard water treatment | "Suitable measures" over 200ppm, without one named product1 |
| Building control notice | Sent by the competent person within 30 days of completion1 |
| Competent person certificate | Reaches you within 8 weeks3 |
GOV.UK notes that Gas Safe is "not technically" one of these schemes, though its installers carry the same building regulations responsibilities in practice4. See building rules for a new boiler for dated detail and weather compensation for how that control works.
2 Cleaning and protection
Baxi's quick start guide says a power flush removes sludge, rust and debris from pipes and radiators, an inhibitor protects the system after cleaning, and a magnetic filter collects magnetic debris before it enters the boiler2. It says its warranty does not cover damage caused by sludge2. That filter deals with sludge in the heating water, not limescale. The rule itself says to clean and flush circuits and add a chemical inhibitor; it does not say a power flush1. More under sludge, inhibitor and filters.
3 Words that often confuse
A "scale reducer" is one possible hard water treatment, and a quote may offer a different one. Ask how it meets the rule; see hard water treatment. "55°C" belongs to new or fully replaced systems under para 5.10 in the 2021 edition, not to a boiler swap on existing radiators as the wording reads1. "Heat loss calculation" is a stated sizing approach only in the 2026 edition, from 24 March 20275. It is a reasonable question to ask now, but not a current rule.
VAT is listed as standard rate for energy-efficient boilers unless a grant-funded route applies, under HMRC's notice6. A quote showing a different rate should say why.
Sources
- Part L Volume 1 for dwellings, England, Table 6.2, paras 5.10, 5.15, 5.20-5.25, 6.2, 8.5, 8.8 and glossary read 3 November 2026.
- Sludge and filters page, p8, quick start for Baxi's Combi 2 range, 7876395-01 read 3 November 2026.
- Building approval through a competent person scheme, GOV.UK read 3 November 2026.
- Competent person schemes: current schemes and how they are authorised, GOV.UK read 3 November 2026.
- 2026 edition, Volume 1 Dwellings, England, note under para 4.9 read 3 November 2026.
- Notice 708/6, HMRC, section 2.23 and section 3, updated 31 January 2024 read 3 November 2026.