New Boiler Installation London: Gas Safe Quotes

Most London homes still burn gas, so a like-for-like swap is the common job. The decision that matters is the type: combi, system or regular. That comes down to the number of bathrooms, your mains water flow and whether there's space for a cylinder.

Get at least three fixed quotes and line them up item by item. Our new boiler cost guide has national price ranges to check them against.

London at a glance

Water hardness: Hard. Thames Water, which supplies most of London, says all the water in its region is hard (200 to 300 mg/l of calcium carbonate) or very hard (over 300 mg/l). Source
Homes that are flats: 54.0% of London households (1.8 million) lived in a flat, maisonette or apartment in 2021, against 21.7% across England and Wales. Source
How homes are heated: 70.5% of London households heat with mains gas only, 12.6% with electricity only and 3.4% from a communal or district heat network. Oil-only heating is 0.1%, about 4,300 homes. Source
Energy ratings: About 42% of homes with an EPC in London are rated band D or below (median score 70, band C), against 47% across England. Based on certificates lodged in the 10 years to March 2025. Source

Matching the boiler to the home

54% of London households live in a flat. For a one or two bedroom flat with a single bathroom, a combi is usually right: no tanks, no cylinder cupboard, hot water on demand.

A combi is only as good as the mains feeding it. Ask the installer to measure the flow rate at the kitchen tap before quoting, because upper floors of older blocks can have weak pressure that no combi will fix.

Protection against London's hard water

Thames Water classes all its water as hard, so ask what the installer fits to protect the new heat exchanger. Look for a scale reducer on the cold supply, a magnetic filter on the heating return and inhibitor in the system water. They cost little next to the boiler and help keep the warranty intact.

Questions for every quote

Does the price include a system flush, a new flue, rerouting the condensate pipe and taking the old boiler away? In a flat, does a new flue position need the freeholder's consent? Many leases treat outside walls as the freeholder's property.

Your installer should notify the job through the Gas Safe Register, which leads to a Building Regulations compliance certificate from your council. Keep it with the warranty paperwork; buyers' solicitors ask for it.

Is another gas boiler the right call?

If the home suits one, a heat pump with the £7,500 Boiler Upgrade Scheme grant can be a real alternative. Our heat pump pages for London cover what the outdoor unit needs and when planning rules apply.

Which boiler suits which London home

Victorian and Edwardian terraces

Terraces with a loft conversion and two bathrooms often outgrow a combi. A system boiler with an unvented cylinder runs two showers at once, but find the cylinder space before you commit.

Converted flats and mansion blocks

Fitting the new boiler where the old one hung is usually the cheapest route. Moving it can mean new gas pipe, a new flue route and a longer condensate run.

Outer-borough 1930s semis

Swapping an old regular boiler for a combi frees the loft of tanks. If a heat pump is on your list for later, keeping a cylinder may save work down the line.

Areas covered

Engineers who cover London work across areas including Islington, Hackney, Camden, Brixton, Wimbledon, Ealing, Croydon, Walthamstow, Greenwich and Richmond.

View London on Google Maps

Questions people in London ask

How long does a boiler swap take?

A like-for-like combi swap usually takes one or two days. Changing the boiler type or moving it to another room adds time.

Sources

Also nearby: Boiler installation in Reading, Boiler installation in Luton, Boiler installation in Chelmsford, Boiler installation in Brighton

All boiler installation locations →