The short answer
The single non-negotiable is Gas Safe registration: any engineer who installs or works on a gas boiler in the UK must be registered with the Gas Safe Register. Beyond that, look for manufacturer accreditation (for the best warranty terms), itemised quotes, a site visit before quoting, and a clear description of what is included. See installation cost breakdown to understand what a proper quote covers.
Choosing a boiler installer is as important as choosing the boiler itself. A well-specified boiler fitted badly by an underqualified engineer will underperform and fail early; a standard boiler fitted excellently by an experienced professional will outperform expectations. This checklist gives you the questions to ask and the red flags to watch for when comparing quotes.
Installer checklist at a glance
- Non-negotiable Gas Safe registered (check gassaferegister.co.uk)
- Manufacturer accreditation Unlocks 10-yr warranty (Worcester, Vaillant)
- Minimum quotes At least three, itemised
- Site visit Engineer should visit before quoting, not just phone
- Documents issued Gas Safe cert + Benchmark Checklist on completion
- Red flag No Gas Safe number; quote without site visit
Gas Safe registration: the legal baseline
In the UK, it is illegal for anyone to carry out gas boiler work who is not registered with the Gas Safe Register. Gas Safe replaced Corgi registration in 2009 and is the official UK gas registration body. Every registered engineer carries a Gas Safe ID card that shows their unique licence number and the categories of gas work they are qualified to do. Before any engineer starts work, ask to see their card or check their registration online at gassaferegister.co.uk using their licence number. Do not accept verbal assurances — a licence number is easy to check and takes 60 seconds. An unregistered engineer cannot legally issue a Gas Safe installation certificate, and work done without certification is unsafe and will affect your home insurance.
Manufacturer accreditation
If you are considering a Worcester Bosch or Vaillant boiler with a 10-year warranty, the engineer must also be a manufacturer-accredited installer (Worcester Bosch Accredited Installer or Vaillant Advanced Installer). This is separate from Gas Safe registration — it is the manufacturer’s own qualification. Ask specifically whether the engineer holds the relevant accreditation for the brand you are considering, and verify it if possible. For Ideal boilers, the 7–10 year warranty is available without specific accreditation on most models, making it the more flexible choice for independent engineers.
| Check | How to verify | Why it matters |
|---|---|---|
| Gas Safe registration | gassaferegister.co.uk (licence number) | Legal requirement; safety |
| Worcester Accredited | Worcester Bosch website | Unlocks 10-year warranty |
| Vaillant Advanced | Vaillant website | Unlocks 10-year warranty |
| Public liability insurance | Ask for certificate | Covers damage during works |
| Trustpilot / Google reviews | Online search | Real-world experience from other customers |
Getting and comparing quotes
Get at least three quotes, and make sure each engineer has visited the property (or done a thorough video survey) before quoting — not just a phone estimate based on the number of bedrooms. Quotes should be itemised: boiler unit, flue, labour, magnetic filter, inhibitor, Gas Safe certificate and Benchmark Checklist should all be visible. A quote that just says “£2,400 supply and fit” without a breakdown is harder to compare and easier to dispute if something is missing. When comparing, check that all quotes are for the same boiler model (or a genuinely comparable alternative) and the same scope of work — a quote that omits a magnetic filter appears cheaper but is not, when you add the filter cost.
What to confirm before the installation starts
Before the engineer begins work, confirm: the scope of work (exactly what is included); what happens if additional issues are found on the day (will they quote before proceeding?); what brand and model of boiler will be fitted; what warranty term you will receive and whether they will register it; and how payment is to be made (avoid paying in full before the job is complete). After the installation, check you have received the Gas Safe certificate and the Benchmark Commissioning Checklist before you pay the final balance. If either document is missing, do not consider the job complete. This is general guidance; all gas boiler work must be carried out by a Gas Safe registered engineer and comply with current Building Regulations.
Find Gas Safe registered engineers near you
Compare itemised quotes from Gas Safe registered engineers in your area and confirm Gas Safe registration and manufacturer accreditation before booking.
Frequently asked questions
How do I check if a boiler engineer is Gas Safe registered?
Go to gassaferegister.co.uk and enter the engineer’s licence number. The search takes 60 seconds and confirms their registration status and the categories of work they are qualified to carry out. Always check before work begins.
Should I use a large company or a local sole trader?
Both can offer good service. A large company may offer better aftercare coverage and is more likely to have manufacturer-accredited engineers; a local sole trader may offer more competitive pricing and a more personal service. The key check is Gas Safe registration for either.
How many boiler quotes should I get?
At least three. This gives you a meaningful price range and helps you spot a quote that is suspiciously cheap (possibly missing items) or suspiciously expensive. Make sure all quotes are for the same boiler model and scope of work before comparing prices.
What should I do if a boiler engineer does not give me a Gas Safe certificate?
A Gas Safe certificate must be issued for all gas boiler installations by law. If an engineer has not provided one within a few days of completion, contact them to request it. If they are unable to provide it, report the installation to the Gas Safe Register — and do not use an unregistered engineer in future.
Sources & further reading
- Gas Safe Register — checking engineer registration, what Gas Safe covers, consumer rights
- GOV.UK — competent person schemes and self-certification requirements
- HHIC — Heating and Hotwater Industry Council, consumer guide to choosing a heating engineer
- Energy Saving Trust — getting quotes for a new boiler and what to look for
This is general information, not advice for your specific property or installation. Costs, timescales and outcomes vary with your home, system condition and chosen engineer. All gas boiler work must be carried out by a Gas Safe registered engineer.