New Boiler Installation in London: Complete Cost Guide for 2025

New Boiler Installation Costs in London: 2025 Price Guide

Getting an accurate picture of boiler installation costs in London before you start is essential. Prices vary significantly based on the type of boiler, the brand you choose, how complex the installation is, and whether any additional work such as a system flush or new pipework is needed. This guide breaks down the typical cost ranges for 2025 so you can plan your budget confidently.

Combi Boiler Installation Costs London

A combination boiler (combi) heats water on demand and does not require a hot water cylinder or cold water tank in the loft. Combi boilers are the most common choice for London properties, particularly flats and smaller terraced houses with one or two bathrooms. A typical combi boiler installation in London costs between £1,800 and £2,800 including supply and installation of the boiler, a new flue, system flush and inhibitor dosing, new controls, Building Regulations notification, and a Gas Safe certificate.

The price varies based on brand. A mid-range combi such as an Ideal Logic or Vaillant ecoFIT costs towards the lower end of this range. A Worcester Bosch Greenstar or Viessmann Vitodens, which command premium pricing and offer longer warranties, sits at the top of the range. For properties with multiple bathrooms where hot water demand is high, an output of 30kW or above is usually appropriate.

System Boiler with Unvented Cylinder Costs London

A system boiler works with a pressurised hot water cylinder to provide central heating and stored hot water. This is the preferred choice for larger London properties with two or more bathrooms where simultaneous hot water demand would overwhelm a combi boiler. A system boiler installation with an unvented cylinder in London typically costs between £3,000 and £4,500. The cylinder itself accounts for £600 to £1,200 of this cost depending on size and brand. Unvented cylinders must be installed by an Unvented Hot Water Systems qualified engineer, which Prestige Engineers provides.

Back Boiler to Combi Replacement Costs London

Many London Victorian and 1970s properties still have a back boiler installed behind the fireplace, feeding an old gravity-fed system with a cold water tank in the loft and a hot water cylinder in the airing cupboard. Replacing this type of system with a modern combi involves removing the back boiler, decommissioning and removing the header tank and cylinder, installing the new boiler in a kitchen or utility cupboard, and routing a new flue. This is a more involved job and typically costs between £2,500 and £3,500.

Factors That Affect Your Installation Cost

Several factors can push your installation cost above or below the ranges quoted above. Flue routing is a significant variable. A simple straight flue through an external wall is the cheapest option. A flue that needs to run up through a roof, around corners, or through a shared wall in a flat will add to the labour time and materials cost. In London mansion blocks and purpose-built flats, the managing agent may also require the landlord to use approved contractors for any work affecting shared walls or the building fabric, which can influence contractor choice.

Whether a new gas connection or gas meter upgrade is needed is another major variable. If your current gas meter is not rated for the flow required by the new boiler — a common issue in older properties switching from a back boiler to a high-output combi — a meter upgrade may be required. This is arranged through the gas supplier and typically costs nothing if you are the account holder, though it adds time to the project.

The condition of the existing system also matters. An old system with heavy sludge contamination will require a full power flush before the new boiler is commissioned. Power flushing adds £300 to £500 to the overall cost but is essential to protect the new boiler warranty. Magnetic system filters are typically included in a professional installation and provide ongoing protection.

What Is Included in a Professional Installation

A professional boiler installation from a Gas Safe registered company in London should always include supply and installation of the boiler, a new flue assembly, a magnetic system filter, system inhibitor dosing, full commissioning and testing, new thermostatic controls or smart thermostat integration, Building Regulations compliance notification to your local authority, and a Gas Safe commissioning certificate. Any installer who quotes without including these items should be questioned about what is and is not in the price.

Getting an Accurate Quote from Prestige Engineers

Prestige Engineers provides fixed-price boiler installation quotes for London properties following a site survey. We install Worcester Bosch, Viessmann, Vaillant, and Ideal boilers and are a Worcester Bosch Accredited Installer, giving customers access to up to 12 years warranty. We cover all 33 London boroughs. Contact us for a free, no-obligation survey and written quote.