The short answer
If the boiler in the home you have just bought needs replacing, the best time is between completion and moving day, while the house is empty. Fixed-price online installers quoted, when we checked on 4 October 2026:
- iHeat: £1,745 to £2,445 fitted, including VAT, with next-day installation on most orders placed before 3pm.
- Heatable: boilers from £1,995 fitted.
Those are prices for a like-for-like swap. Moving the boiler to another room, converting from a system or regular boiler to a combi, or replacing radiators adds to the cost - get a quote that reflects your actual house.
First: does it actually need replacing?
Do not replace a working boiler because it is old. Find out what you have:
- Ask the seller for the paperwork. Gas Safe Register advises buyers to ask for the boiler's building regulations compliance certificate and any gas safety records. The certificate shows when it was installed and that it was notified properly.
- Read your survey. A surveyor who could not see a service record, or noted the boiler's age or condition, has told you to investigate.
- Book a gas safety check if there is no recent record. If the seller cannot provide one, or the last check was more than 12 months ago, Gas Safe Register's advice is to have a Gas Safe registered engineer check it before you move in. That visit also tells you whether replacement is worth considering.
Replacement makes sense when the engineer finds the boiler unsafe or uneconomic to repair, when parts are no longer available, or when you want to change the system - for example to a combi in a smaller home.
Why timing it around your move matters
Replacing a boiler in a lived-in home means a day without heating or hot water, dust sheets over the floors, and furniture shifted to reach pipes. Doing it in an empty house avoids all of that:
- Book the installation for the days after completion, before the removal van arrives. iHeat says a standard replacement typically takes one day and other installations one to two.
- Allow a buffer in case the installer finds extra work - a blocked flue or corroded pipework is easier to fix with no one living there.
- If your completion and moving day are the same day, book the install for the first weekday after and plan for a night or two of cold water.
Planning the move itself? Our moving house checklist puts the trades in order, and the moving cost calculator prices the removal.
Online fixed-price installers or a local engineer?
| iHeat | Heatable | Local Gas Safe engineer | |
|---|---|---|---|
| How you get a price | Online questions, about 60 seconds | Online questions, choose a fixed-price package | Home visit, written quote |
| Published price | £1,745–£2,445 fitted, inc. VAT | From £1,995 fitted | Not published |
| Fitting time | Next day on most orders before 3pm | Dates chosen at booking | Depends on the firm |
| Warranty | 5 to 10 years, depending on the boiler brand | 12-month workmanship warranty; ask about the manufacturer's | Varies - ask |
| Finance | 0% APR available | Interest-free and other options | Rarely |
Online installers win on speed and on knowing the price before anyone visits. A local engineer can be cheaper for an awkward job, and is someone you can call back. The sensible approach is to get both online prices, then one local quote, and compare like with like - same boiler brand and model, same warranty length, same scope of work.
Whoever you use, check two things:
- The engineer is on the Gas Safe Register. Both iHeat and Heatable state that their engineers are Gas Safe registered; for a local firm, check the register yourself.
- What the warranty covers. A long manufacturer's warranty usually requires an annual service; a workmanship warranty covers the installation itself. They are not the same thing.
Paperwork after the installation
The installer must notify the new boiler to your local authority within 30 days, and you should receive a building regulations compliance certificate. It belongs to the property, so keep it with your house documents - you will need it when you remortgage or sell. Register the boiler with the manufacturer if the installer has not, so the warranty starts.
Should you consider a heat pump instead?
If you are replacing fossil-fuel heating, the government's Boiler Upgrade Scheme in England and Wales gives £7,500 towards an air source or ground source heat pump, or £5,000 towards a biomass boiler. A heat pump needs a survey to check the house suits one, takes longer to install than a boiler swap, and works best in a well-insulated home - the recommendations on the property's EPC are a good first indication. See which certificates come with a home for where to find it.