Boiler Installation & Replacement in London
Combi, system and regular boiler installation across London. Transparent fixed pricing, Gas Safe certified engineers, correct boiler sizing and 5–10 year warranties.
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Premium pricing for London's finest properties
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Combi boiler installation in London: costs, timelines & what's included
A new combi boiler installation in London typically costs between £1,800 and £4,500 depending on the boiler brand, property size, flue requirements and system complexity. RARE installs Vaillant, Viessmann, ATAG and Worcester Bosch boilers across Central and North West London, with all work Gas Safe certified and manufacturer warranties registered on your behalf.
Modern A-rated combi boilers are up to 30% more efficient than units from 10–15 years ago. If any of the below apply, a replacement could save you money and prevent costly future breakdowns.
A combi boiler replacement in a prime London property is an investment that rewards precision. Selecting the right output rating for your property's heat demand, specifying the correct flue route, and matching the boiler to existing pipework and controls all affect long-term performance. RARE's home survey covers all of these factors before we provide a fixed quote — ensuring the system we install performs exactly as it should for the life of the boiler.
We are approved installers for Vaillant, Viessmann, ATAG, Worcester Bosch and Ideal. As a Gas Safe registered boiler installation company serving London since 2013, our boiler installers handle every aspect of the replacement — from correct sizing to commissioning and warranty registration. For London homes — particularly those in prime postcodes where quiet operation and visual discretion matter — we typically recommend Vaillant's ecoTEC range or ATAG's One series for their combination of output, efficiency and near-silent running.
- Boiler is over 10–15 years old
- Frequent breakdowns and costly repairs
- No hot water or heating on demand
- High energy bills from an inefficient system
- Boiler pressure constantly dropping
- Yellow or orange flames instead of blue
- You have a conventional boiler with an ageing cylinder
- You want smart thermostat and zoned heating control
Get a Survey & Quote
We'll visit your property, assess your requirements and provide a fixed, transparent quote — with no hidden extras.
020 7458 4949Book a SurveyCombi, System Boiler or Plant Room — Which Is Right for You?
Every London home has different heating and hot water demands. Answer six quick questions about your property, bathrooms and hot water usage — we'll recommend the right system for your home, whether that's a compact combi, a system boiler with cylinder, or a full plant room rebuild.
- Tailored recommendation based on your actual property
- Covers combi, system boiler and plant room scenarios
- Instant result — no waiting, no obligation
- Links straight to the right installation page
Which Boiler System Do You Need?
Answer a few questions — get a tailored recommendation
Question 1 of 6
How many bathrooms does your home have?
Including ensuites and cloakrooms
What a correct boiler installation actually involves
Most installers replace the boiler and leave. RARE engineers design the installation around your property's specific heat demand, pipework and controls.
Heat loss calculation
We calculate the heat loss of each room — based on floor area, ceiling height, insulation and glazing — to determine the correct boiler output. A boiler that's too big keeps switching itself on and off, wastes fuel and fails early. We size boilers correctly.
Boiler sizing
The correct output for a London terraced house is typically 24–28 kW. For a larger townhouse with multiple bathrooms and underfloor heating, 35–40 kW may be appropriate. We use the industry-standard heat loss calculation (BS EN 12831) rather than guessing.
Why oversized boilers fail
A boiler too large for your home heats up quickly then shuts off, over and over. This stops it running at its most efficient, wastes gas and causes extra wear. Read our Oversized Boiler Problems guide for more.
Combi vs system boiler
Combi boilers are ideal for properties with 1–2 bathrooms. Larger homes running several showers and taps at once benefit from a system boiler paired with a pressurised Megaflo hot water cylinder. We recommend the right solution for your specific demand.
Smart controls & weather compensation
We set up weather compensation on compatible boilers — the boiler automatically adjusts its heat based on the outdoor temperature, for genuine efficiency gains. We also install Heatmiser, Tado and Honeywell for room-by-room scheduling.
Water quality & system flush
Every installation includes a system flush and a magnetic filter to catch debris. London's hard water causes limescale to build up inside the boiler. We also advise on protective chemicals and water softeners where helpful.
Pipework upgrades
Older pipework that's too narrow or has corroded joints can restrict flow and cause noise. We identify and upgrade problem sections during installation — extending the life of your new boiler.
System balancing
After installation, we balance all radiators to ensure even heat distribution across every room. An unbalanced system overheats some rooms while others remain cold — wasting fuel and comfort.
Gas Safe certification
All gas work is carried out by Gas Safe registered engineers. You receive a Gas Safe certificate, Building Regulations Compliance Certificate and full appliance documentation before we leave.
Boiler installation — what you need to know
What size boiler do I need?
Boiler size is determined by a heat loss calculation, not by the number of radiators. A typical London terraced house needs 24–28 kW; a larger townhouse with multiple bathrooms may need 35–40 kW. An oversized boiler short-cycles — firing and shutting off repeatedly — which wastes gas and shortens the boiler's life. RARE calculates heat loss room-by-room using BS EN 12831 methodology before specifying a boiler. Use our heat loss calculator for an indicative estimate.
What is the best boiler for a large house?
For larger London homes with multiple bathrooms, a system boiler paired with an unvented hot water cylinder (such as a Megaflo) is usually the correct choice — it delivers mains-pressure hot water to several outlets simultaneously. A combi boiler struggles to meet high simultaneous hot water demand. For properties with underfloor heating or a plant room, a cascade configuration may be appropriate. See our system boiler installation page for larger properties.
Can a combi boiler supply two showers?
A combi boiler can supply two showers in sequence, but running both simultaneously will usually result in reduced flow at each outlet. If two or more bathrooms need hot water at the same time, a system boiler with an unvented cylinder (Megaflo) is the correct specification — it stores hot water at mains pressure and delivers full flow to every outlet simultaneously. We assess your actual demand at survey before recommending a system type.
When should I replace my boiler?
Replace your boiler when it is over 10–15 years old, breaking down repeatedly, costing more in repairs than its remaining value, or when your energy bills are noticeably higher than they should be. A modern A-rated boiler is up to 30% more efficient than a unit from 15 years ago. If your boiler is still reliable but you are renovating or extending, a planned replacement avoids disruption later. See our boiler replacement guide for a detailed assessment.
Combi, System & Regular Boilers
The right boiler type depends on your property, not a one-size-fits-all answer. RARE installs all three types — and recommends the correct one based on your hot-water demand, property size and existing system.
Combi Boilers
An all-in-one unit that provides heating and instant hot water without a cylinder. Compact and efficient — the most common choice for London flats and homes with 1–2 bathrooms.
- No cylinder or loft tank needed
- Compact — fits in a kitchen cupboard
- Best for 1–2 bathrooms
- Instant hot water on demand
System Boilers
Paired with an unvented hot water cylinder (Megaflo, OSO) for stored hot water at mains pressure. The right choice for homes with 2+ bathrooms and high simultaneous hot-water demand.
- Mains-pressure hot water to every outlet
- Simultaneous showers and baths
- Ideal for 2+ bathrooms
- Requires a hot water cylinder
Regular (Conventional) Boilers
For period and listed properties with existing vented systems and a loft cold water tank. We can replace like-for-like or upgrade to a combi or system boiler where appropriate.
- Suits period & listed properties
- Works with existing vented systems
- Can be upgraded to combi or system
- Loft tank required
Heating & Hot Water System Design
A boiler is the heart of a heating system — not a standalone appliance. Before recommending a boiler, RARE engineers assess the whole property to ensure the boiler, cylinder, pipework and controls work together correctly. We size for your actual heat and hot-water demand, not a guess. Most installers replace the equipment and leave. RARE designs the installation around your property.
Property & Demand
- Property size and layout
- Heat requirement (kW)
- Number of bedrooms
- Number of bathrooms
- Number of occupants
- Expected simultaneous hot-water usage
Water System
- Incoming mains pressure
- Incoming mains flow rate
- Existing pipe sizes
- Existing cylinder (if present)
- Direct vs indirect configuration
- Recovery times and boiler output
Heating System
- Existing boiler make, model & output
- Heating zones
- Underfloor heating integration
- Radiator sizing and layout
- Smart controls & weather compensation
- System balancing requirements
Practical Considerations
- Plant-room / cupboard space
- Flue route and condensate arrangements
- Future maintenance accessibility
- Water quality and hardness
- Building regulations compliance
- Warranty registration
System Boiler + Unvented Cylinder — designed together
Many premium London properties — townhouses, mansion flats and homes with multiple bathrooms — need a properly designed combination of a system boiler and an unvented hot water cylinder. The boiler heats the home and re-heats the cylinder; the cylinder stores hot water at mains pressure for simultaneous showers and baths. Getting this combination right means sizing both components together based on actual demand, not installing them in isolation.
Combi Boiler Alone
Heats water on demand without a cylinder. Compact and efficient — ideal for flats and homes with 1–2 bathrooms where simultaneous hot water use is limited.
- No cylinder needed
- Compact footprint
- Best for 1–2 bathrooms
- Limited simultaneous hot water
System Boiler + Cylinder
The boiler heats radiators and re-heats the cylinder. The cylinder stores hot water at mains pressure — delivering simultaneous hot water to every bathroom. The right solution for homes with 2+ bathrooms.
- Full mains pressure at every outlet
- Simultaneous showers and baths
- Ideal for 2+ bathrooms
- Boiler and cylinder sized together
Cylinder Upgrade
Replacing a vented cylinder with an unvented Megaflo or OSO delivers mains-pressure hot water without changing the boiler. Effective when the existing boiler is still serviceable.
- Mains pressure without new boiler
- Removes loft cold water tank
- Faster hot water recovery
- Boiler must have adequate output
Need a cylinder too? See our Hot Water Cylinder Installation page
For homes with multiple bathrooms, a system boiler paired with an unvented cylinder is often the right solution.
Brands We Install
We recommend the right boiler for your property — not the one with the highest margin. All brands come with full manufacturer warranties.
Vaillant
German engineering, A-rated efficiency
Viessmann
Premium quality, up to 10yr warranty
Worcester Bosch
UK's most trusted boiler brand
ATAG
Ultra-quiet, highest efficiency ratings
Ideal
Reliable, great value for money
Keston
Specialist high-efficiency condensing boilers
Our Installation Process
From survey to Gas Safe sign-off — every installation follows our proven 6-step process.
Home Survey
We visit your property to assess the existing system, pipework, gas supply and hot water demand before recommending the right boiler.
Fixed Quote
You receive a transparent, itemised quote with no hidden call-out charges. No surprises on installation day.
Remove Old Boiler
We drain down the system, safely disconnect and remove the old boiler, cylinder (if applicable) and associated pipework.
System Flush
Before fitting the new boiler, we power flush or chemically flush the system to remove sludge and debris that could damage your new unit.
Install & Commission
The new combi boiler is fitted, connected and fully commissioned — including fitting a magnetic filter, testing all controls and verifying gas pressure.
Certify & Hand Over
We issue your Gas Safe certificate, register the warranty and walk you through the controls — leaving you with full documentation.
What our clients say
"RARE replaced our ancient back boiler with a Vaillant combi. The whole job was done in a day, the engineer was spotless and the difference in hot water pressure is unbelievable."
Caroline H.
Marylebone
"Competitive quote, arrived exactly on time, left the house immaculate. Gas Safe cert came through the same evening. Will absolutely use RARE again."
David K.
St John's Wood
"We had three quotes and RARE were the most transparent. No upselling, honest advice and a first-class installation. The new Viessmann is whisper quiet."
Emma R.
Primrose Hill
Boiler Installation Calculator
Get an indicative price. RARE pricing reflects our premium expertise and white-glove London service — fixed quotes within 24 hours.
Boiler Installation Calculator
Premium pricing for London's finest properties
Step 1 of 5
What type of installation?
Select your boiler type to begin
Combi Boiler Questions Answered
Everything you need to know before booking a combi boiler installation in London.
Still have questions?How We Work
Every engineer. Every visit. Every time.
01
We listen and understand the issue
We hear your concerns in full before forming any opinion about the cause.
02
We inspect properly before making assumptions
Diagnostic tools and a thorough assessment come before any recommendation.
03
We protect your home before starting work
Floor coverings are laid and surfaces protected before a single tool is lifted.
04
We record work clearly with notes and photographs
Every job is photographically documented — before, during and after.
05
We explain the outcome before leaving
We confirm what was done, what was found and any recommended next steps.
Serving London's most iconic neighbourhoods.
Our engineers are established across prime London — near landmarks including Berkeley Square, Harrods, Eaton Square, Regent's Park and Hampstead Heath.
Boiler installation — complete topic guide
Boiler Repairs
24/7 emergency & planned repairs
Vaillant Boiler Repairs
London's Vaillant specialists
Viessmann Boiler Repairs
Vitodens series experts
ATAG Boiler Repairs
ATAG One & Q series
Boiler Replacement Guide
Repair vs replace explained
Boiler Installation Costs
Full London pricing guide
Power Flushing
Required before new boiler install
Smart Thermostats
Heatmiser, Tado & Honeywell
System Boiler Installation
For larger homes & plant rooms
Central Heating
Full system installation
Hot Water Cylinder Installation
Megaflo, OSO & unvented cylinder specialists
Megaflo Installation & Repairs
G3-qualified Megaflo cylinder specialists
Heat Loss Calculator
Size your boiler correctly
PPM Maintenance
Protect your new boiler
Get a Boiler Quote
Fixed price in 3 steps
Related reading from our Knowledge Hub
Reviewed by RARE Plumbing London Engineering Team
Gas Safe Registered Heating Engineers · Reviewed 1 September 2026
Authoritative Sources & References
- WikipediaCentral heating — Wikipedia
Wikipedia — Encyclopaedic overview of central heating systems, heat generation, circulation methods and the history of whole-building heating.
- WikipediaBoiler — Wikipedia
Wikipedia — Reference on the design and operation of closed-vessel boilers used for central heating and hot water generation.