Installing a new boiler is a major expense for any household. In 2025, the average cost for a straightforward combi boiler replacement in the UK is between £2,500 and £4,500. This price includes the boiler itself, the flue, system filters, and the labor from a Gas Safe registered engineer.
The type of boiler is a major cost driver. A combi boiler is generally the most common and cost-effective for most homes. A system boiler, which requires a separate hot water cylinder, or a conventional boiler with a cylinder and a cold water tank, will typically be more expensive to install. The brand of the boiler also affects the price, with brands like Worcester Bosch, Vaillant, and Viessmann being at the premium end, while Ideal and Baxi offer more budget-friendly options.
The complexity of the installation will also impact the final cost. If you are moving the boiler to a new location in your home, this will require significant new pipework and will increase the price. Converting from an old conventional system to a modern combi boiler is also a more complex job that will be at the higher end of the price range.
Always ensure your installer is on the Gas Safe Register, as it is illegal for anyone not registered to work on gas appliances. Get several detailed quotes and check what warranty is offered on both the boiler and the workmanship.