How much does boiler installation cost in London?

In London in 2026, a like-for-like combi boiler swap typically costs £1,950–£3,200 fully fitted, including the boiler, installation, system flush, smart thermostat and a 10-year manufacturer warranty. A full system conversion (e.g. regular to combi) usually runs £3,200–£4,800 because of the extra pipework, controls and a new gas supply where required. Prices vary with boiler brand and output, your existing system, and access constraints in flats versus houses.

What you're actually paying for

A boiler installation quote isn't just the cost of the boiler — it's the labour, the system flush, the pipework changes, the new controls, the certification and the warranty registration. In London, where most jobs are in occupied homes with restricted access and Building Control notification requirements, the labour and compliance cost is a significant share of the bill.

A typical fixed-price install in London for 2026 covers: the boiler itself (e.g. Worcester Bosch, Vaillant, Ideal), a system flush to remove sludge, a magnetic filter, a smart thermostat (Nest, Hive or similar), all flue and gas pipework, a Gas Safe Building Control notification, and the manufacturer's extended warranty registration.

Combi boiler swap (like-for-like): £1,950–£3,200

If you already have a combi boiler in roughly the right place, a like-for-like swap is the cheapest option. The new boiler can usually go in the same spot, using the existing flue exit and pipework with minor modifications.

Where you sit in this range depends mainly on the brand and output you choose. An Ideal Logic Max 30kW typically sits at the lower end; a Worcester Bosch 8000 Style 35kW with a 12-year warranty sits at the top.

System or regular boiler swap: £2,400–£3,800

If you have a system boiler (boiler plus hot water cylinder, no cold tank in the loft) or a regular boiler (boiler, cylinder and a cold tank), a like-for-like swap costs slightly more than a combi swap because of the extra controls and the cylinder connections.

For larger London houses with multiple bathrooms, a system or regular boiler with a vented or unvented cylinder usually outperforms a combi — and so swap is the right call rather than a full conversion.

Full conversion (regular → combi): £3,200–£4,800

Removing a cold water tank from the loft, scrapping the cylinder and converting to a combi is more invasive. You're typically running new gas pipework, capping off old feed pipes, removing tanks and decommissioning the old cylinder space.

It frees up a hot press and a loft tank, and is hugely popular in London Victorian terraces with newly converted lofts. Expect 1–2 days of work and slightly more disruption than a like-for-like swap.

What can push the price up

Common cost-adders on London installs: a new gas supply from the meter (£300–£800 depending on run), a flue extension or vertical flue kit (£150–£450), magnetic filter and chemical flush upgrades, new TRVs on every radiator, and additional Building Control or freeholder permissions in leasehold flats.

Ask any installer to break these out separately on the quote, so you can see exactly what's optional and what's required.

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