Boiler Installation London: 2026 Costs, Brands, and What to Expect

How much a new boiler costs in 2026

Across South London, a fully fitted boiler installation in 2026 typically lands somewhere between £2,200 and £5,500. That is the all-in figure: the boiler itself, the flue, controls, magnetic filter, fittings, labour, system flush, and commissioning. The wide range reflects three things: the type of boiler, the brand and model, and how much pipework needs altering on the day.

A like for like combi swap, where the new boiler goes on the same wall as the old one and the gas and water connections are already in roughly the right place, sits at the lower end. Expect £2,200 to £3,000 for a budget brand combi (Ideal Logic, Baxi 600, Glow-worm Energy) and £2,800 to £3,800 for a premium combi (Worcester Bosch Greenstar, Vaillant ecoTec Plus). A system boiler with a new unvented cylinder is usually £4,000 to £5,500 because of the extra cylinder cost, the labour to fit it, and the discharge pipework that has to run to outside.

Anything that involves moving the boiler to a new location, converting from a system to a combi, or swapping a back boiler in a cupboard for a wall mounted unit pushes the price up. Moving the boiler to the loft or the garage is usually £400 to £900 on top, depending on the route the gas pipe needs to take. Converting a regular system to a combi often means removing the cold water tank from the loft and the hot water cylinder from the airing cupboard, which adds about half a day of work.

In older terraces around Lewisham, Bromley, and Croydon, we often find the gas supply pipe is 15mm when the new boiler needs 22mm to run at full output. Upgrading the gas pipe from the meter to the boiler is a common extra and adds £150 to £400 depending on length and access. A power flush, which is sometimes needed on systems older than ten years, adds £400 to £600 but is often the difference between a boiler that lasts fifteen years and one that fails in five.

If you want a written quote rather than a ballpark, our team can survey the property and price the job properly. Use the boiler quote form or call us on 020 3576 2747.

Combi vs system vs regular boiler

There are three boiler types and the right one depends on how much hot water you use, how many bathrooms you have, and what the existing setup looks like.

Combi boilers

A combi heats hot water on demand. There is no cylinder and no cold water tank in the loft. You turn on the tap, the boiler fires, and hot water comes out. This works well for flats and houses with one bathroom, or two bathrooms used at different times. A 30kW to 35kW combi can usually run a shower and a kitchen tap together but struggles if two showers run at the same time. Around 70 percent of London installations are combis.

System boilers

A system boiler heats a stored cylinder of hot water (usually unvented, pressurised mains fed). You can run multiple showers at the same time without pressure dropping, which makes it the right choice for three bedroom houses and up with two or more bathrooms. The cylinder takes up space, usually in an airing cupboard. You also need to run a discharge pipe from the unvented cylinder to outside.

Regular (heat only) boilers

The traditional setup with a hot water cylinder and a cold water tank in the loft. We do not recommend installing a new regular boiler in 2026 unless the existing system is so unusual that converting would be prohibitively expensive. They take more space and are less efficient than the modern alternatives.

If your current setup is regular and you have decent water pressure at the mains, converting to a combi or to a system boiler is usually worth the extra cost. You free up the airing cupboard, lose the loft tank, and end up with a more efficient setup. Our plumbing services page covers conversion work in detail.

Installation timeline

A straightforward combi swap, where the boiler stays in roughly the same position, takes one working day. We arrive between 08:00 and 09:00, drain the existing system, remove the old boiler, fit the new one, run a system flush, refill, commission, and walk you through the controls before we leave. The heating is usually back on by late afternoon.

A boiler relocation (moving from kitchen to loft, for example) takes one and a half to two days. The extra time covers running new gas and water pipework and dealing with the flue route through the roof.

A full system conversion, removing tanks and a cylinder and converting to a combi, usually takes two and a half to three days. Day one strips out, day two fits the new boiler and pressurises the system, day three is for commissioning, balancing radiators, and any plasterwork repairs where the old tank or cylinder used to be.

We register every install with Gas Safe within 30 days, which sends the building regulations certificate to your local authority automatically. You also get the manufacturer warranty registered on the day, which is what gives you the long warranty terms.

Finance options

Most boiler installers offer finance through a third party, usually Novuna or Tandem. Typical options in 2026 are 0 percent over 24 months on smaller jobs, or 9.9 percent APR over 5 to 10 years on larger installations. We can arrange finance on quoted jobs if you want to spread the cost.

Before you sign up to any finance, check whether your local authority runs a warm homes grant. Some South London boroughs run small top up grants for replacing very old boilers, particularly for owner occupiers over 60 or households on certain benefits. Croydon, Greenwich, and Lewisham have all run schemes like this in recent years.

For landlords, the cost of a new boiler is fully deductible against rental income in the year it is spent, since it counts as a repair (replacing like with like) under HMRC rules. Speak to your accountant for specifics, but it is normally treated more favourably than a capital improvement.

How to choose a Gas Safe installer

Anyone who works on a gas boiler in the UK has to be on the Gas Safe Register. Working on a gas appliance without registration is illegal. Before you let anyone install or service your boiler, ask for their Gas Safe ID card and check the number on the Gas Safe Register website.

Beyond the legal minimum, here are the things worth checking:

• Are they accredited with the boiler brand? Brand accreditation usually unlocks the longest warranty terms (10 to 12 years).
• Will they put the quote in writing with a fixed price, not an estimate?
• Does the quote include a system flush, magnetic filter, and TRVs on every radiator? These should be standard, not extras.
• Do they register the install with Gas Safe and the manufacturer on the day?
• How long is the labour warranty (separate from the manufacturer warranty)?
• Do they carry public liability insurance? Ask for proof.

We are Gas Safe registered, accredited with Worcester Bosch and Vaillant, and every quote we send is fixed price with no day rate ambiguity. Our installers cover the whole of South London including Bromley, Croydon, Orpington, Lewisham, Greenwich, and the surrounding Kent boroughs.