heating
Boiler installation and replacement
Replacing a domestic boiler costs £1,900 to £3,600 fitted for a straight combi swap, and £3,200 to £5,500 where the system is being converted or the boiler moved. The boiler itself is under half of that figure; the rest is labour, controls, and the pipework the new appliance needs.
What this covers
What it costs. A combi boiler replacement costs £1,900 to £3,600 fitted. Full cost breakdown.
What the job covers
- Swapping a combi boiler like for like
- Converting a conventional system to a combi
- Moving a boiler to a different room
- System boiler and cylinder installations
- Registering the work with Gas Safe and building control
What is involved
A like-for-like swap keeps the boiler in the same place on the same pipes, and takes one or two days. The installer drains the system, lifts the old appliance out, adapts the gas, water and flue connections, fits a magnetic filter on the return, chemically flushes or power flushes the system, and commissions the new boiler against the manufacturer's gas rate and flue gas analysis figures. That commissioning is not optional paperwork: an incorrectly gas-rated boiler either runs short of output or runs rich, and both shorten its life.
A conversion is a different job. Going from a conventional system with a hot water cylinder and two loft tanks to a combi means removing the cylinder and tanks, capping the vent and cold feed, running a new mains cold supply capable of a decent flow rate, and often upgrading the incoming main from 15mm to 22mm. That last point decides whether a combi is the right answer at all. A house with a 12 litre per minute mains supply will never give two good showers from a combi, and a system boiler with an unvented cylinder is the honest recommendation.
Any gas work has to be done by a Gas Safe registered engineer, and the installation has to be notified to building control. Most installers do this through the Gas Safe building regulations notification, and the certificate should land with you within a few weeks. Keep it: it is what a future buyer's solicitor asks for.
Swapping a combi boiler like for like, one of the jobs a boiler installation specialist is hired for.
Choosing someone for the job
Ask for the mains flow rate in litres per minute before anyone recommends a combi. Ask whether the quote includes a magnetic filter, a chemical flush or a power flush, and new controls. Ask which Gas Safe registration number the work will be notified under, and check it on the Gas Safe register. A quote that does not name the boiler model and output in kilowatts is not a quote.
Common questions
How long does a boiler replacement take?
A straight swap is usually one day, occasionally two. A conversion from a cylinder system to a combi is two to three days because tanks come out and pipework changes.
Do I need a power flush with a new boiler?
Not always. On a system in reasonable condition a chemical flush and a magnetic filter satisfy most manufacturers' warranty terms. A power flush is worth it where radiators are cold at the bottom or the water runs black.