The short answer
A boiler installation quote covers the unit, flue, labour, commissioning, a Gas Safe certificate and disposal — add magnetic filter, inhibitor and potentially a power flush or pipework changes. Knowing what each line should cost helps you compare quotes on the same basis. For the headline ranges, see new boiler costs.
When you receive boiler installation quotes, prices can vary by hundreds of pounds between engineers — sometimes for what looks like the same job. The difference is rarely just labour rate; it is what is and is not included. This breakdown explains what every element of a properly specified installation should cost, so you can read a quote with confidence and spot anything that has been omitted or inflated.
Installation cost elements
- Boiler unit £600–£1,800 depending on brand & output
- Labour (1 day) £500–£900
- Flue & fittings £80–£250
- Magnetic filter £80–£150 (if not included)
- Gas Safe certificate Included in compliant quote
- Benchmark commissioning Included in compliant quote
The boiler unit
The largest single cost in most quotes is the boiler itself. Trade prices differ from retail prices, so an engineer buying through a merchant will typically pay less than the RRP you see online. A good installer will pass on some of that margin rather than marking up to full retail; a poor one will charge full retail and also charge for labour on top. If you can see a trade price (many merchants publish them), you can sanity-check the unit cost in a quote. Budget combis typically cost £600–£900 at trade; mid-range models £900–£1,200; premium models £1,200–£1,700.
Labour
A standard like-for-like combi swap in a day typically involves: isolating and removing the old boiler; fitting the new unit; connecting the gas, flow and return, and condensate; fitting or reusing the flue terminal; filling and pressurising the system; and commissioning. An experienced sole-trader Gas Safe engineer typically charges £500–£700 for this day’s work; a larger installation company typically charges £700–£900, partly reflecting overheads and partly the peace of mind of a company with insured aftercare. London and South-East rates sit 10–20% above the national average. Two-day jobs — involving a flush, a conversion or a relocation — double or more the labour element.
| Line item | Typical cost | Notes |
|---|---|---|
| Boiler unit (mid-range) | £900–£1,300 | Trade price; varies by brand & output |
| Labour (1 day) | £500–£900 | Sole trader vs company |
| Flue terminal & fittings | £80–£200 | Standard horizontal; longer runs more |
| Magnetic filter | £80–£150 | Often included by better installers |
| Inhibitor dose | £20–£40 | Protects system from corrosion |
| Gas Safe certificate | Included | Must be issued; request your copy |
| Benchmark Checklist | Included | Required for manufacturer warranty |
| Old boiler disposal | Included | F-gas handling if applicable |
| Power flush (if needed) | £300–£500 | Only if sludge is evident |
Flue and fittings
A standard horizontal flue kit for a wall-mounted combi costs £80–£120 and is sometimes included in the boiler price. Non-standard flues — longer runs, bends, vertical flues through a roof, or concentric flue systems — require additional components and labour. Budget £150–£400 for non-standard flue arrangements. The flue must terminate in a compliant position under Building Regulations Part J; an engineer placing it below a window or too close to an opening would be non-compliant.
Certifications and documentation
Two documents must be issued on completion of any new boiler installation by a Gas Safe registered engineer: the Gas Safe certificate (also called the RIDDOR/Gas Safety Record) confirming the installation is safe; and the Benchmark Commissioning Checklist, completed by the engineer when setting up the boiler, which confirms it has been correctly commissioned and is required by most manufacturers to validate the warranty. Neither should cost extra — if an engineer suggests charging for these separately, treat that as a red flag. Always ask for your copy of both and keep them safe. See our guide on what to expect during installation for what happens on the day. This is general information; exact costs depend on your property, boiler choice and location, and all gas work must be carried out by a Gas Safe registered engineer.
Compare itemised boiler quotes
A fully itemised quote makes comparison straightforward. Use our service to get quotes from Gas Safe registered engineers who itemise their costs.
Frequently asked questions
What should be included in a boiler installation quote?
A complete quote should include the boiler unit, flue terminal and fittings, one day’s labour, a magnetic filter, inhibitor, Gas Safe certificate, Benchmark Commissioning Checklist and removal of the old boiler. Always ask for an itemised quote so you can compare fairly.
Why do boiler installation prices vary so much?
Prices vary because quotes bundle different things. One engineer may include a magnetic filter, inhibitor and extended labour; another may quote the boiler and basic fitting only. Comparing on the same specification is essential. Location also matters — London rates are 10–20% higher.
Is a Gas Safe certificate included in the installation price?
It should always be included in a compliant installation. A Gas Safe certificate is a legal requirement for all gas boiler installations, not an optional extra. If an engineer charges separately for it or does not mention it, ask for clarification.
What is a Benchmark Commissioning Checklist?
The Benchmark Checklist is the industry-standard document completed by the engineer when setting up a new boiler. It records the system settings and test results and is required by most boiler manufacturers to validate the warranty. You should receive a copy on installation day.
Sources & further reading
- Gas Safe Register — Gas Safe certificate requirements and installer obligations
- HHIC — Benchmark Commissioning Checklist guidance
- Energy Saving Trust — new boiler costs and what affects them
- GOV.UK / Building Regulations Approved Document J — combustion appliances and fuel storage systems
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.