A new boiler can improve your EPC rating, because the heating and hot water system is one of the inputs an energy assessor records. It is not the only input. Insulation, glazing, the hot water cylinder and the heating controls feed the same calculation. Nobody can tell you in advance how many points or bands a boiler swap will gain. An EPC in England and Wales is valid for 10 years, and a new one appears only when somebody commissions an assessor. This page covers what the assessor records, when a fresh EPC is worth commissioning, and which boiler papers a buyer's solicitor asks for.
Does a new boiler improve your EPC rating, and by how much?
A new boiler can lift your EPC rating, because the heating system is one of the installations the certificate is based on. An EPC runs from A, very efficient, down to G. It is calculated from the construction and type of the building together with installations such as heating, insulation and glazing. A replacement boiler changes one of those inputs, not the walls, the loft or the windows.
Nobody can promise you a band in advance. The size of the change depends on what the old system was, what replaces it and what else the assessor records on the day. Your current certificate gives a clue, because every EPC carries a recommendation report of measures that could improve the rating, together with a potential rating if they are carried out. Where the certificate describes the boiler as inefficient, the government guide says this usually points to an older appliance near the end of its working life.
A new boiler is one input in the EPC calculation, not the whole score. What a buyer's solicitor can actually check is the paper trail: the building regulations compliance certificate for the installation, the manufacturer's warranty registration and the service history.
What an energy assessor records about your boiler, controls and cylinder
An energy assessor measures the property, notes how it is built, and records the heating and hot water system before entering everything into approved software. Only an assessor registered with a government-approved accreditation scheme can produce a valid EPC. For a hot water cylinder the assessor records the volume, plus either a measured heat loss factor or the type and thickness of the insulation. A well-insulated cylinder therefore counts towards the result alongside the boiler itself.
Heating controls are part of the same picture. Time and temperature control, weather compensation and load compensation all shape how the system is described in the assessment. An EPC assessment is a survey of the whole dwelling, not an inspection of the appliance. Nothing inside the boiler casing is opened during it.
Do you need a new EPC after replacing the boiler?
A valid EPC can be reused within its 10-year life, so replacing a boiler does not automatically produce a new one. GOV.UK sets the test plainly: you need a new certificate if you have done something that affects the rating. A boiler swap changes the heating system, and a fresh assessment is the only way to get that change onto the certificate. An EPC is also only valid while no newer certificate has been registered for the same building.
When you sell in England and Wales, the duty comes from the Energy Performance of Buildings (England and Wales) Regulations 2012. You must make a valid EPC available to a prospective buyer free of charge, at the earliest opportunity. If no valid certificate exists, you have to commission one before the property goes on the market. The energy rating must also appear in commercial advertisements for the property, and you can download your existing certificate from the government's find an energy certificate service.
Replace the boiler before marketing, or leave it to the buyer?
Both routes are lawful, and the difference shows up in the certificate and in your sale file rather than in any promised outcome. The table sets out what changes for the EPC, the paperwork and who organises the work.
| Point of difference | You replace the boiler before marketing | The buyer replaces it after completion |
|---|---|---|
| Heating entry on the EPC | A fresh assessment can record the new boiler, controls and cylinder; the old certificate stays unchanged until an assessor is commissioned. | The certificate still shows the existing boiler, which the government guide links to an older appliance near the end of its life. |
| Building regulations certificate | Issued to you within 8 weeks of completion by a scheme-registered installer, and it sits in your sale file. | Issued to the buyer after they own the property, so nothing is added to the papers you hand over. |
| Who organises the work | You book the survey, agree a written fixed price and have the old boiler taken away before viewings start. | The buyer chooses the appliance, the installer and the timing once the sale has completed. |
| Conveyancing questions | You answer the TA6 property information form with the certificate and warranty registration to hand. | There is no recent boiler certificate to supply, and the buyer makes their own arrangements. |
Neither route guarantees anything about price or how a sale proceeds. What you can decide is which papers exist in your file at the point of marketing.
Which boiler paperwork a buyer's solicitor asks for
A buyer's solicitor looks for the building regulations compliance certificate covering the boiler. Replacing a boiler is notifiable building work. It is either self-certified by an installer registered with a competent person scheme, or notified to the council with a building notice at least 48 hours before work starts.
A scheme-registered installer notifies the work and issues a certificate within 8 weeks of completion, and that record appears in the solicitor's searches when the house is sold. Where an earlier boiler was never notified, the council holds no evidence of compliance, and compliance certificates can be asked for during the sale. The regularisation route covers work that was already carried out. Our guide to the building regulations compliance certificate explains which document you should hold.
The seller's Property Information Form (TA6), with TA7 added for a leasehold, is where these certificates, guarantees and warranties are listed. Buyers also ask about servicing, which is covered in our guide on boiler service records and gas safety certificates when selling.
What Boiler Plus requires when a boiler is replaced in England
Boiler Plus has applied in England since 6 April 2018, as part of Approved Document L of the Building Regulations. A gas boiler fitted under it must be at least 92% efficient, with a boiler interlock plus time and temperature control, where those are not already present and working. A combi boiler needs one further efficiency measure as well: load compensation, weather compensation, smart controls with automation and optimisation, or flue gas heat recovery.
There is no opt-out. A boiler fitted without these measures is not building regulations compliant. Those same controls are part of what an energy assessor records, so Boiler Plus and the EPC pull in one direction.
Work on the gas supply, the flue or anything inside the boiler casing is for a Gas Safe registered engineer under the Gas Safety (Installation and Use) Regulations 1998 as amended. As a householder you can read the boiler pressure gauge and top it up, check the thermostat and programmer settings, use the reset button and bleed radiators. Everything else on the appliance is the engineer's work.
What changes for gas boilers under the reformed EPC from October 2026
The reformed EPC for homes replaces the single headline figure with four metrics: energy cost, fabric performance, heating system and smart readiness. The heating system metric scores the efficiency and carbon intensity of heating and hot water. Under that metric, heat pumps and low-carbon heat networks are expected to reach C or better, while gas, oil and LPG boilers cannot reach C. The government aims to introduce the new certificates from October 2026, with an implementation plan being developed alongside the industry.
No prediction is possible for a specific house. The selling duty itself does not change: you must make a valid EPC available, not fit a particular heating system. A gas boiler replacement remains a lawful installation, and what the reform changes is how the certificate describes it. If you are weighing up a replacement before marketing the property, a free home survey and a written fixed price come before any work on a new boiler installation.
Sources
- The Energy Performance of Buildings (England and Wales) Regulations 2012, Part 7
- Selling a home: Energy Performance Certificates – GOV.UK
- A guide to Energy Performance Certificates for the marketing, sale and let of dwellings – GOV.UK
- Technical annex for chapter 2: What EPCs measure – GOV.UK
- Reforms to the Energy Performance of Buildings regime: partial government response – GOV.UK
- Building regulations approval: use a competent person scheme – GOV.UK
- Boiler Plus: new standards for domestic boiler installations from April 2018 (PDF) – GOV.UK