A like-for-like combi boiler replacement means swapping your old combination boiler for a new one in the exact same spot, using the existing gas, water, and flue connections without rerouting pipework. In London, this is the fastest and most affordable way to restore heating and hot water, with prices starting from £1,050 and most jobs completed in 4 to 6 hours on the same day.
If your combi boiler has broken down, is losing pressure constantly, or has simply reached the end of its 10 to 15-year lifespan, this guide will walk you through exactly what to expect, how much you should pay, and how to avoid the common traps that catch London homeowners out.
What Does “Like-for-Like” Actually Mean?
In plain terms: your new combi boiler goes where the old one sat, connects to the same pipes, and uses the same flue route. Nothing moves. No walls come down. No new cylinder or water tank appears in your airing cupboard.
This matters because boiler jobs fall into three distinct categories, and each one changes the price dramatically:
| Job Type | What Happens | Typical Cost in London |
|---|---|---|
| Like-for-like replacement | New combi in the same position, existing pipework | From £1,050 |
| System conversion | Switching from combi to system boiler + cylinder | From £3,500 |
| Relocation | Moving the boiler to a different room or wall | Added to base cost |
The key difference is labour. A straight combi-to-combi swap avoids the heavy building work, extended pipe runs, and structural changes that drive costs up. The engineer removes the old unit, cleans the system, fits the new one, tests everything, and hands over your Gas Safe certificate. That is it.
How Much Does a Combi Boiler Replacement Cost in London?
A like-for-like combi boiler replacement in London starts from £1,050. Most homeowners in the capital pay between £1,800 and £3,500 when they receive quotes from national firms or independent engineers, but that wide range usually reflects hidden mark-ups, unclear specifications, or sales commissions rather than the actual work involved.
Here is an honest breakdown of where your money goes:
| Cost Component | What It Covers | Typical Price |
|---|---|---|
| Boiler unit | A-rated combi from a reputable brand | £600 – £1,200 |
| Labour & fitting | Removal, installation, testing, certification | £400 – £800 |
| System flush | Power flush or chemical clean to protect the new boiler | Included |
| Magnetic filter | Traps sludge and protects against London’s hard water | Included |
| Thermostat & controls | Digital or smart thermostat fitted and paired | Included |
| Assessment visit | In-person survey to confirm the exact price and boiler model | £100 |
Why Some Quotes Are Higher
London property stock is old. Victorian and Edwardian homes often have narrow boiler cupboards, awkward flue runs, or pipework that no longer meets current gas regulations. An installer cannot see these details over the phone. That is why a £100 assessment visit exists: it confirms the exact combi boiler replacement cost for your specific home before any work is booked, so you are not hit with surprise extras on fitting day.
How Long Does a Like-for-Like Boiler Replacement Take?
Most combi-to-combi swaps take 4 to 6 hours and are completed in a single day. You will have heating and hot water restored before the engineer leaves.
The timeline looks like this:
- Arrival & isolation (30 mins) — Gas and electrics safely turned off; old boiler drained.
- Removal (45–60 mins) — Old unit disconnected, lifted out, and responsibly disposed of.
- System preparation (30–45 mins) — Existing pipework inspected; flush carried out if needed.
- Installation (90–120 mins) — New boiler mounted, gas and water connections made, flue secured.
- Testing & commissioning (45–60 mins) — Pressure tests, gas tightness tests, safety checks, and thermostat pairing.
- Certification (15 mins) — Gas Safe certificate issued; manufacturer warranty registered.
Delays only happen when the existing pipework is corroded, the flue does not meet current standards, or access is severely restricted. The assessment visit is designed to spot these issues in advance.
What’s Included in a Standard Replacement?
A proper boiler swap london service should include more than just screwing a new box to the wall. Here is what you should expect as standard:
- Safe removal and disposal of your old boiler, including environmentally responsible recycling of the metal and components.
- New combi boiler fitted in the same position, connected to existing gas, water, and flue pipework. Any worn fittings are replaced as needed.
- Full system flush to clear debris and sludge from your existing radiators and pipework.
- Magnetic filter installation to catch future debris and protect the heat exchanger from London’s notoriously hard water.
- Digital thermostat or smart controls fitted and paired. If you already own a smart thermostat like a Nest or Hive, the engineer should reconnect it.
- Gas Safe certificate issued on the same day before the engineer leaves.
- Manufacturer warranty registration so your 5 to 10-year parts and labour cover is active immediately.
If a quote does not mention the flush, filter, or certificate, ask why. Cutting corners on any of these shortens the life of your new boiler and can invalidate your warranty.
Is Your Home Suitable for a Combi-to-Combi Swap?
Not every home qualifies for a like-for-like replacement. You are almost certainly eligible if:
- You already have a combi boiler (no hot water cylinder or cold water tank in the loft).
- You are happy with the current location and do not want it moved.
- Your gas supply pipe is adequate for the new boiler’s output.
- Your flue terminates safely on an external wall and meets current regulations.
You will need a system conversion instead if:
- You currently have a conventional boiler with a cylinder and tanks, and you want to keep that setup.
- You have a back boiler fitted behind a fireplace.
- Your property has very low mains water pressure, which makes a combi impractical.
- You are switching from combi to system boiler because you have added multiple bathrooms.
The simplest way to check? Send a photo of your current boiler and cupboard to a Gas Safe registered installer on WhatsApp. They can tell you within minutes whether you qualify for a straight swap or need something more complex.
Best Boiler Brands for a Straight Swap
For a fast combi boiler replacement london job, you want a unit that fits standard kitchen cupboards, connects easily to existing pipework, and comes with a long warranty. These are the brands London engineers fit most often:
Worcester Bosch
The market leader for reliability. Their Greenstar range fits most standard cupboard sizes and comes with up to a 10-year warranty when fitted by an accredited installer. Ideal if you want peace of mind and strong resale value for your property.
Vaillant
German engineering with excellent after-sales support. The ecoTEC range is compact, quiet, and works well in flats and terraced houses where space is tight. Slightly pricier than entry-level models, but the build quality shows.
Ideal
The Logic and Vogue ranges offer the best balance of price and performance. A popular choice for landlords and first-time buyers who need a dependable boiler without paying a premium. Warranties run from 7 to 12 years depending on the model.
Baxi
A solid British brand with straightforward controls and easy servicing. Good for older properties where the engineer wants familiar, widely available spare parts.
Output sizing tip: Most 2 to 3-bedroom London homes need a 24kW to 30kW combi. Larger homes with 4+ bedrooms or multiple bathrooms may need 35kW+. The assessment visit confirms the right size for your hot water demand.
Why Choose Like-for-Like Over a System Conversion?
Homeowners often assume they need to “upgrade” to a system boiler when their combi fails. In reality, if your current setup works for your lifestyle, a straight swap is usually the smarter choice.
| Factor | Like-for-Like Swap | System Conversion |
|---|---|---|
| Cost | From £1,050 | From £3,500 |
| Time | Same day | 1–3 days |
| Disruption | Minimal; no building work | Significant; new cylinder, pipework, possibly loft work |
| Space | No extra space needed | Requires cupboard or airing cupboard for cylinder |
| Hot water | On-demand, but flow limited by mains pressure | Stored hot water, better for multiple simultaneous showers |
A system conversion only makes sense if you have added bathrooms, your mains pressure is too low for a combi, or you specifically want stored hot water. For the average London flat or 2-bed terraced house, a new combi boiler fitted same day london is the practical, cost-effective route.
The £100 Assessment: What Happens and Why It Matters
Some installers quote fixed prices over the phone, then add hundreds of pounds in “extras” once they arrive. A £100 assessment fee removes that uncertainty.
During the 30 to 45-minute visit, the engineer checks:
- The exact boiler model and its position.
- The flue type, length, and termination point.
- The condition of existing gas pipework and whether it meets current regulations.
- Water pressure and flow rates.
- Access to the property (parking, stairs, cupboard dimensions).
You receive one firm, written quote. If you go ahead, the £100 is typically deducted from the final bill. If you decide not to proceed, you have only paid for the engineer’s time and expertise. It is a small price for avoiding a £2,500 surprise.
How to Book a Same-Day Boiler Replacement in London
If you have no heating or hot water right now, speed matters. Here is the fastest route from broken boiler to warm radiators:
- Message a Gas Safe registered installer with a photo of your current boiler, its make/model if visible, and your postcode.
- Book the £100 assessment for the same day or next day. Most reputable firms offer emergency boiler replacement london slots within 24 hours.
- Receive your fixed quote at the assessment. Ask about the boiler brand, warranty length, and exactly what is included.
- Schedule the fitting. If it is a straightforward combi-to-combi swap, the engineer can often return the same day or the following morning.
- Get your certificate and warranty before the engineer leaves. Store both digitally and physically.
Red flags to avoid: Installers who refuse to show their Gas Safe card, demand full payment upfront, or cannot provide a written quote with a company address and VAT number.
Frequently Asked Questions
What does “like-for-like” boiler replacement mean?
It means replacing your existing combi boiler with a new combi boiler in the exact same location, using the current gas, water, and flue connections without moving or extending pipework. No cylinder, no tank, no building work.
How much does a combi boiler replacement cost in London?
A like-for-like combi boiler replacement cost 2026 starts from £1,050 in London. The final price depends on the boiler brand, output size, condition of existing pipework, and flue type. An in-person assessment confirms the exact figure.
How long does a like-for-like boiler replacement take?
Most jobs take 4 to 6 hours and are finished in a single day. You will have heating and hot water restored before the engineer leaves, assuming no hidden issues with the existing installation.
Can I replace my combi boiler with another combi?
Yes, provided you are happy with the current location, your gas supply is adequate, and your flue meets regulations. This is the most common and affordable type of boiler replacement for London homes.
What is included in a combi boiler replacement?
A standard package includes removal and disposal of the old unit, fitting the new boiler, a system flush, magnetic filter, digital thermostat, Gas Safe certificate, and warranty registration. Always confirm this list in writing before booking.
Do I need a Gas Safe certificate for boiler replacement?
Yes. It is a legal requirement in the UK for any gas boiler work to be carried out by a Gas Safe registered engineer, and you must receive a Building Regulations Compliance Certificate within a few days of completion. Reputable engineers issue this on the same day.
Is a boiler assessment visit necessary?
For an accurate quote, yes. Even simple swaps can hide complications like corroded pipework or non-compliant flues. The £100 assessment ensures you receive one firm price with no surprises on fitting day.
What is the cheapest way to replace a combi boiler in London?
A like-for-like swap is the cheapest way to replace a combi boiler london homeowners can choose. Avoiding pipework changes, relocations, or system conversions keeps labour costs low. Booking directly with a local Gas Safe installer rather than a national sales company also cuts out middleman commissions.
Can a boiler be replaced in one day?
Yes. A standard combi-to-combi replacement in the same position is almost always completed within a single working day, typically 4 to 6 hours. System conversions or relocations take longer.
What boiler brand is best for a small flat in London?
For flats and smaller homes, compact models like the Worcester Bosch Greenstar CDi Compact, Vaillant ecoTEC Plus, or Ideal Logic Plus are excellent choices. They fit standard kitchen cupboards, run quietly, and offer strong warranties.
Final Thoughts
A failing boiler is stressful enough without confusing quotes, hidden costs, and weeks of waiting. A like-for-like combi boiler replacement london offers the simplest path back to reliable heating and hot water: same position, same type, same day, and from £1,050.
The key is honesty. Know what you need. Know what it should cost. And know who you are letting into your home. Always check the Gas Safe Register, demand a written quote, and make sure your warranty and certificate are sorted before the van leaves.
If your combi boiler is on its way out and you want a straightforward, fairly priced swap with no surprises, book a £100 assessment with a local Gas Safe registered engineer. You will have a fixed quote in person and, in most cases, a warm home by the end of the day.