Evo Plumbers logo
Call now
✓ Gas Safe registered● 24/7 emergency line● Covering all of London
← Back to blog

Gas Boiler Installation in London: Cost, Steps and Rules

Engineer checking a newly installed gas boiler

A new gas boiler in a typical UK home costs roughly £2,500 to £4,000 fully fitted, and the work must be done by a Gas Safe registered engineer who quotes the whole job before starting. If you want that handled in London by engineers who are Gas Safe registered and who give a fixed price before work begins, our boiler installation service covers homes, landlords and businesses across the capital, 24/7 if the old boiler fails in an emergency.

This guide explains what the price covers, what happens on the day, how to choose between a combi and a system boiler, and which certificates you should be handed at the end.

Evoplumbers
evoplumbers.com
Plan Your Boiler Installation
Evo Plumbers installs boilers across London, with Gas Safe registered engineers and fixed quotes before work begins.
Visit

TL;DR

  • A standard gas combi replacement typically runs from £2,500 to £4,000 including boiler, flue, controls, labour and commissioning, according to a 2026 UK market report.
  • Fitting a gas boiler is legally restricted to qualified engineers: check the Gas Safe ID card before any work starts.
  • A good quote is in writing and names the boiler, the pipework, the flue, the flush and the labour, so there are no surprises on the invoice.
  • In England a replacement gas boiler must meet a 92% efficiency minimum and come with proper controls.
  • Expect a Building Regulations certificate, a commissioning record and the manufacturer’s warranty paperwork at handover.

Table of Contents

What a gas boiler installation actually includes

A full installation is more than swapping one metal box for another. The boiler itself is only part of the bill. The job usually covers:

  • removing and disposing of the old boiler;
  • mounting the new boiler and connecting gas, water and heating pipework;
  • fitting a flue, the pipe that carries combustion gases safely outside;
  • fitting controls such as a thermostat and timer;
  • cleaning the heating system and adding a filter and inhibitor;
  • commissioning, meaning testing that the boiler burns safely and runs as designed.

The quote you accept should list each of these. If an item is missing, ask whether it is included or will be added later.

How much does a new boiler installation cost?

The UK Boiler System Installation Market report, published in July 2026, puts a standard gas combi replacement, with boiler, flue, controls, labour and commissioning, at between £2,500 and £4,000. Premium brands such as Worcester Bosch, Vaillant and Viessmann sit at the upper end. A system boiler with a hot water cylinder adds £500 to £1,000. The same report says construction-sector inflation has added 10 to 15% to labour charges since 2020.

These are national figures for the year of publication. London jobs depend on the property, access and what has to change, so treat them as a guide to the range, not a quote.

What moves the price

A 2026 price guide lists the same set of drivers that engineers weigh up on a survey:

  • Boiler brand and output. Better-known brands and higher outputs cost more.
  • Pipework changes. Moving the boiler to another wall or room means new gas and water runs.
  • The flue route. A flue that has to be re-routed, extended or taken through a different wall takes more time and parts.
  • System cleaning and filters. Older heating systems often need a thorough flush and a magnetic filter.
  • Boiler type. Converting a regular or system boiler to a combi involves removing the tanks and cylinder and re-piping.

Labour is the largest single element, which is why the quote matters more than the boiler’s sticker price. A suspiciously low figure often leaves out the flush, the controls or the flue.

Why a fixed quote protects you

The most common complaint about boiler work is a price that grows once the old boiler is off the wall. That is why we quote every job at a fixed price before work starts: you know the total, you approve it, and you pay on completion. Our prices are set per job after we know the property, so we do not publish a single figure, but the quote you receive covers the whole scope in writing.

Combi, system or regular: which boiler suits your home?

The choice comes down to how much hot water you use at once and what is already installed.

Boiler type How it works Suits
Combi Heats water on demand from the mains, no tank needed Flats and small to medium homes with one or two bathrooms
System Heats a stored cylinder, no loft tanks Larger homes with several bathrooms
Regular Uses a cylinder and loft tanks Older properties with existing tank-fed systems

Gas Safe Register notes that combi boilers can be cheaper to install because many homes do not need a separate hot water storage cylinder, as they heat water after it enters the boiler from the cold-water main. It also explains that hot-water performance depends on mains water pressure and flow, and that flow can drop if several taps run at once when the system is not designed for it. That is why a good engineer checks your mains flow and the number of bathrooms before recommending a combi, rather than fitting one by default.

If the property is a small London flat, a combi usually frees up the airing cupboard. If a family of five shares two showers, a system boiler with a cylinder may serve better.

Step by step: what happens during an installation

A like-for-like combi replacement is typically a one-day job. Changing type or moving the boiler takes longer, often two days. Here is the sequence and where each stage goes wrong if rushed.

  1. Survey and quote. The engineer looks at the existing boiler, flue, pipework, gas supply and your hot water needs. This is where the scope is fixed. Where it goes wrong: a quote given over the phone without seeing the property, which then changes on the day.
  2. Preparing the house. Clear access to the boiler, the cupboard and the route to the flue. Dust sheets go down and the water and gas are isolated. Where it goes wrong: poor access slows the job and can add hours.
  3. Removing the old boiler. The system is drained and the old unit disconnected and taken away. Where it goes wrong: the old pipework turns out to be corroded or undersized, which is why a survey matters.
  4. Fitting the new boiler and flue. The boiler is mounted, the flue is fitted to safety standards and gas, water and heating pipes are connected. Where it goes wrong: an incorrectly sited flue is a carbon monoxide risk, and a regulated gas job is no place for improvisation.
  5. Cleaning the system. The Centre for Sustainable Energy says the installer should flush the heating system, by power flush or mains pressure flush depending on the model, to remove sludge and deposits, and may add scale inhibitors. Where it goes wrong: skipping the flush lets old sludge into a new heat exchanger, which shortens its life.
  6. Testing and commissioning. The engineer checks gas tightness, combustion and controls, then sets the boiler up. Where it goes wrong: no commissioning record, which can affect the warranty.
  7. Handover. You are shown the controls, the pressure gauge and how to reset the boiler, and receive your paperwork.

The same Centre for Sustainable Energy guidance stresses that flushing and annual servicing are what keep a new boiler efficient and reliable, so book the first service for twelve months after installation.

Who may fit a gas boiler, and what to check first

It is illegal, and potentially extremely dangerous, for someone who is not fully qualified to fit a central heating boiler, as the Centre for Sustainable Energy states. In practice that means a Gas Safe registered engineer. So the answer to “can I install my own boiler?” is no: gas work is for registered engineers only.

Before work starts, Gas Safe Register advises that you check the engineer’s Gas Safe ID card shows they are qualified for the gas work you need. The same page recommends confirming the job in writing, including:

  • the agreed price and scope of work;
  • the appliances and materials included;
  • how and when you pay;
  • any subcontractors and their Gas Safe numbers;
  • the start date, how long it will take and any late penalties;
  • the Building Control notification or certificate, where it applies.

It also suggests checking that the business holds public liability insurance. Our engineers are Gas Safe registered, and we put the job in a fixed-price quote before work begins.

Building Regulations and efficiency rules in England

A boiler installation is notifiable work under Building Regulations. The Centre for Sustainable Energy explains that an installer on a Competent Persons Scheme can self-certify compliance; if they are not, you need approval from your council or a registered building control approver. Either way you should end up with a certificate, which you will want when you sell the property.

Three technical rules shape what goes in:

  • Efficiency. Since 6 April 2018, replacement gas boilers in existing homes in England must reach at least 92% seasonal space heating efficiency, with boiler interlock and time and temperature controls on every new gas or oil boiler installation.
  • Extra energy saving measure for combis. The same installer guide says a combi in an existing home must include at least one of: flue gas heat recovery, weather compensation, load compensation or a smart thermostat with automation and optimisation.
  • Carbon monoxide alarms. Approved Document J, as amended in 2022, includes guidance on providing carbon monoxide alarms where gas burning appliances are installed.

These apply in England. Rules in Scotland, Wales and Northern Ireland differ, but for a London home these are the ones that matter.

Landlords: installation and gas safety

If you let a property, a new boiler is also a compliance event. The Gas Safety (Installation and Use) Regulations 1998 require checks and records, including recording defects and remedial action, and the records are kept for two years from the date of the check. A new installation does not replace the annual landlord gas safety check, so keep the installation certificate with your gas safety records. Our guide to the gas safety check explains what it covers, who needs one and how it fits with the work.

For tenants, a new boiler that arrives with a commissioning record and a clean system is the simplest way to avoid repeat breakdowns and no-hot-water complaints. If you are in that situation now, see what to check when there is no hot water.

Landlords: installation and gas safety

Replace or repair?

A boiler that overheats repeatedly, loses pressure, leaks or cannot be repaired economically is a candidate for replacement. If yours is overheating, our guide to boiler overheating causes and warning signs shows what to do straight away. If you smell gas or suspect a carbon monoxide leak, turn off the gas at the meter, open windows, leave the property and call the National Gas Emergency Service on 0800 111 999.

Boiler installation with Evo Plumbers

We install boilers for homeowners, landlords and businesses across London. Our engineers are Gas Safe registered, every job is quoted at a fixed price before work starts, and you pay when the work is complete. If your boiler fails outside office hours, calls are answered 24/7.

Evoplumbers

To get a fixed quote, start from our boiler installation page or see the local pages for Putney, Battersea, Acton, Hammersmith and Fulham. For the gas side of a wider job, our gas works page covers the rest.

Our view: the quote is the installation

Most boiler problems we hear about are not about the boiler. They are about the gap between what was promised and what turned up on the day: a flue that was not in the price, a flush nobody mentioned, a certificate that never arrived.

That is why we work the other way round. A Gas Safe registered engineer looks at the job, we give a fixed price before work starts, and you pay when it is finished. The price you approve is the price you pay.

A new boiler is a safety-critical gas appliance in your home. It deserves a properly scoped job, a clean system, correct controls and the paperwork to prove it was done right. We would rather you chose on those terms than on the lowest headline figure.

the author

FAQ

How much does a gas boiler installation cost?

A standard gas combi replacement typically ranges from £2,500 to £4,000 including the boiler, flue, controls, labour and commissioning, according to a 2026 UK market report. A system boiler with a cylinder adds £500 to £1,000. We give a fixed quote for your property before any work starts.

No. Fitting a central heating boiler by someone who is not fully qualified is illegal and can be extremely dangerous, as the Centre for Sustainable Energy says. Use a Gas Safe registered engineer and check their ID card before work begins.

How long does a new boiler installation take?

A straightforward like-for-like combi swap is usually completed in a day. Converting from a regular or system boiler to a combi, or moving the boiler, takes longer because pipework and the old cylinder and tanks are involved. The survey establishes the time before you agree the quote.

Do I need to have the system flushed?

The Centre for Sustainable Energy says the installer should flush the system when fitting a new boiler to remove sludge and deposits. A clean system protects the new boiler and is part of a properly scoped quote.

What paperwork should I get afterwards?

You should receive a Building Regulations compliance certificate, the commissioning record and the manufacturer’s warranty details. Keep them with your property records. Landlords should file them alongside their gas safety records.

Sources

Lines open 24/707771 604654WhatsApp