Most people who ask us this have an old boiler that has started to worry them and want a straight answer before they ring anyone. This page gives you that answer as honestly as we can, explains what actually moves the price, and tells you how to get a fixed figure for your own house without any obligation.
The short answer
For a straightforward like-for-like combi swap in South East London, the market price in 2026 is broadly somewhere in the region of £1,800 to £3,000, fully fitted. That is a guide range taken from what installers across the area charge, not a quote. Your own figure depends on the boiler you choose and the state of what is already on the wall.
If the job involves changing the type of system, moving the boiler, or replacing a lot of pipework, the range moves up. Converting an older house from a boiler-and-cylinder set-up to a combi commonly lands between about £3,000 and £4,500, and can go higher in a large property. Again, a guide, not a promise.
We give every customer a fixed written price after a free survey. Nothing is added on the day.
What you are actually paying for
A new boiler price is really four things added together. Understanding them is the quickest way to tell a fair quote from an inflated one.
1. The boiler itself
The biggest single item. Prices vary a lot between brands and between models within a brand. A higher output boiler (needed for bigger houses or homes with more than one bathroom running at once) costs more than a smaller one. Premium brands cost more than mid-range ones, and usually come with longer manufacturer warranties. We install Worcester Bosch, Vaillant, Ideal, Baxi, Viessmann and Potterton and we will tell you plainly which one makes sense for your house rather than pushing the dearest.
2. Labour
A like-for-like swap is usually a one-day job for a Gas Safe engineer. A system change, a relocation, or a property with awkward access takes longer and costs more in labour. In South East London terraces and flats, access and flue routing are the two things that most often turn a one-day job into a two-day one.
3. The parts around the boiler
This is where quotes differ most, and where a cheap headline price can hide extras. A proper installation normally includes some or all of the following, depending on what is already there:
- A new flue and terminal, and sometimes a plume kit if the flue exit is close to a window or a neighbour's boundary
- A magnetic system filter to catch sludge before it reaches the new boiler
- A chemical flush of the radiators and pipework, with inhibitor added, or a power flush if the system is badly sludged
- A condensate pipe run to a drain, insulated if it goes outside
- Controls that meet the current Building Regulations for England (a new combi has to be fitted with time and temperature control plus an energy-saving measure such as a smart or weather-compensating thermostat)
- A gas supply pipe upgrade where the existing run is too small for a modern combi, which is common in older houses that were originally piped for a smaller boiler
4. Paperwork and registration
The installation must be notified to Gas Safe so that you receive a Building Regulations compliance certificate. The manufacturer's warranty has to be registered, normally within a set number of days of the installation. A reputable installer includes both. Ask if it is not written down.
What makes the price go up
If you want to know why one house is quoted more than the neighbour's, it is almost always one of these:
- Moving the boiler. Taking it from a kitchen to a loft, or from a bedroom cupboard to the kitchen, means new gas, water and flue runs. It is the single biggest cost driver after the boiler itself.
- Changing the system type. Going from a heat-only boiler with tanks in the loft to a combi means removing the tanks and cylinder and re-piping the hot water. More labour, more materials.
- A vertical flue. If the boiler cannot vent straight out through an outside wall, the flue goes up through the roof. That adds parts, and sometimes scaffold.
- An undersized gas pipe. Many South East London homes have a gas run that was fine for the boiler fitted twenty years ago and is too small for the one going in now. It has to be upgraded to be safe and compliant.
- A badly sludged system. If radiators are cold at the bottom and the water runs black, a power flush protects the new boiler and its warranty. It costs more than a chemical flush.
- Making good. Boxing in, tiling, plastering around an old boiler position. Some installers include it, many do not. Ask.
What makes the price go down
Keeping the boiler in the same place, keeping the same type of system, and having a flue that can go straight out through the wall are the three things that keep a replacement at the cheaper end. That is what the trade calls a like-for-like swap, and it is the most common job we do. If your existing boiler is in a sensible spot and the system works, do not let anyone talk you into moving it just because it is "better". We have written a separate guide on like-for-like swaps versus full upgrades.
How to compare quotes properly
Three quotes is sensible for a job this size. When you compare them, check that each one states:
- The exact boiler make, model and output
- Whether a flush and a filter are included, and which type of flush
- Whether the price includes controls that meet the regulations, or whether that is extra
- The length of the manufacturer warranty and what it depends on (many longer warranties require an annual service by a Gas Safe engineer)
- Gas Safe notification and warranty registration
- Removal and disposal of the old boiler
- Whether the figure is fixed or an estimate
A quote that is a few hundred pounds cheaper but leaves out the flush, the filter or the controls is not cheaper. It is incomplete.
Is it worth replacing, or should you repair?
If the boiler is under ten years old, the fault is minor and parts are available, a repair is usually the right call. If it is past twelve or fifteen years, has needed more than one repair recently, or the part it needs is no longer made, replacement is usually the better use of the money. We do both, so we have no reason to steer you one way. If you are not sure, read our guide to the signs a boiler will not make it through the winter, or book a £90 boiler service and ask the engineer for a straight opinion while he is there.
Getting a fixed price for your house
We survey for free, price the job in writing, and the figure we give is the figure you pay. We are based in Bromley and install across South East London, including Lewisham, Catford, Brockley, Forest Hill, Sydenham, Blackheath, Bromley and Beckenham. Send us a photo of your current boiler and your postcode on WhatsApp and we will tell you what we think before anyone comes out. See our main new boiler installation page for what is included.
Thinking about a new boiler? We give you a fixed written price after a free survey, and nothing is added on the day.
See our boiler installation service or get in touch for a free quote.