How much does a new boiler cost in London?

Honest London prices, written by the engineers who fit them. No hidden upsells, no commission games. Here's what a new boiler actually costs in 2026, what drives the price up or down, and how to spot a quote that's too good to be true.

Quick answer, typical London boiler prices (inc VAT, fitted)

What's included in a properly priced installation?

Any quote should explicitly include all of the following. If a competitor quote excludes any of these, you're not comparing like-for-like.

• The boiler itself, with manufacturer warranty registered to your address
• Power flush of the existing system (or magnetic filter + chemical clean as a minimum)
• Magnetic system filter (Adey MagnaClean, Fernox TF1) on the return line
• System inhibitor (Sentinel X100, Fernox F1)
• New flue terminal with weather guard
• Wiring centre and timer/controls (or smart thermostat if specified)
• Removal and environmentally-compliant disposal of old boiler
• Gas tightness test, flue gas analysis, commissioning per manufacturer spec
• Building Regulations notification via Gas Safe Register (Compliance Certificate within 30 days)
• Manufacturer registration (so warranty starts on installation date)
• Customer hand-over with controls walk-through and printed manuals
• 12-month workmanship guarantee

What drives the price up?

Boiler model and warranty length

Higher-tier models (Worcester Greenstar 4000/8000, Vaillant ecoTEC plus, Viessmann Vitodens 100/200) cost £400,1,200 more than entry-level units (Ideal Logic, Baxi 200). The premium typically buys you longer warranties (10,12 years vs 2,5 years), better modulation (more efficient at part-load), and more accessible parts in 10-15 years' time.

Boiler relocation

Moving the boiler from its current location to a new one (e.g. from a kitchen to an airing cupboard) typically adds £350,650 inc VAT for gas pipe extension, flue route alteration, condensate routing and electrical re-wiring.

Flue route complexity

A standard horizontal through-wall flue is included in most quotes. But if you need a vertical flue through the roof, an extended flue exceeding 1m, or a plume-management kit (because the flue terminates near a window or property boundary), expect £200,500 additional.

System upgrades and pipework

Older 1970s installations sometimes have ½ inch (15mm) primary pipework that restricts modern boiler output. We'd recommend upsizing to 22mm, typically £300,700 additional depending on accessibility.

Smart thermostat installation

Hive, Nest, Tado and Honeywell all add £140,280 for the unit and installation, depending on whether it's wired or wireless and whether it includes hot-water control.

Power flush vs chemical flush

Power flush is more thorough (specialist Magnacleanse / Kamco-style equipment, 4,6 hours on site). Some installers offer a cheaper "chemical clean" instead, fine for clean systems, inadequate for sludged ones. Power flush typically £450,650 inc VAT if priced separately.

How to spot a quote that's too cheap

• Boiler-only price quoted, no flush, no filter, no inhibitor. Sludge from the existing system will destroy the new heat exchanger within 18 months, and void the manufacturer warranty.
• No mention of Building Regs notification. If the installer isn't notifying Gas Safe Register, the work is illegal and your warranty is void.
• "Cash discount available." Means the work is going off-books, no VAT invoice, no warranty registration, no proof for property sale.
• Fitter is "Gas Safe registered" but won't show the card. Always verify on gassaferegister.co.uk before letting anyone touch your gas.
• "Same-day install" with no survey. A proper installation needs a heat-loss calculation and pressure test. Turn-up-and-fit installers don't do this.

How to choose the right boiler for your London property

If you have 1 bathroom and reasonable mains pressure (1.5+ bar)

A combi boiler, single unit providing heating + instantaneous hot water. Worcester Greenstar 30Ri or Vaillant ecoTEC plus 832 typical choices. £2,400,3,200 fitted.

If you have 2+ bathrooms or low mains pressure

System boiler + unvented cylinder. The cylinder gives you simultaneous-use hot water (two showers running at once). Megaflo, Telford or Heatrae cylinders most common. £4,200,5,800 fitted depending on cylinder size.

If you have a Victorian or Edwardian terrace

Often the existing pipework is undersized for a modern combi. Worth surveying mains pressure and flow before committing, sometimes a system boiler with cylinder is the right answer even for a 1-bath house. We do this calculation properly before quoting.

If you live in a leasehold flat

Check your lease, many require managing-agent consent for boiler replacement (especially flue routing through external walls). We handle the consent paperwork.

0% finance and grants in London

• 0% APR finance over 24 months available on most installations over £1,500. Decisions usually within 24 hours.
• Boiler Upgrade Scheme (BUS), government grant of up to £7,500 for switching from gas to a heat pump. Not applicable to gas-to-gas replacement.
• ECO4 (Energy Company Obligation), free or subsidised boiler replacement for low-income households on certain benefits. Eligibility checked via your energy supplier.

FAQ

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