A straightforward like-for-like combi boiler replacement usually takes around 4 to 6 hours and is normally finished within one working day. More involved jobs — changing your boiler type, moving it to a new location, or reworking pipework — can take 1 to 3 days, depending on your property and heating system.
Below, we break down installation times by boiler type, explain what can push a job into a second or third day, and cover what actually happens on installation day so you know what to expect before a heating engineer arrives.
How Long Does a New Boiler Installation Take?
Most boiler installations in London take between 4 hours and 3 days, and the biggest factor is whether the job is a simple swap or a more complex change to your heating system.
Here’s a quick overview of typical timeframes:
| Installation Type | Typical Time |
|---|---|
| Like-for-like combi boiler swap | 4–6 hours |
| Combi boiler in a new position | 6–8 hours |
| System boiler replacement | 6–8 hours (1 day) |
| Regular (conventional) boiler replacement | 1 day |
| Regular-to-combi conversion | 1.5–2 days |
| System-to-combi conversion | Up to 3 days |
| Boiler relocation (new room or cupboard) | 1–2 days |
These figures are general industry estimates. Your Gas Safe registered engineer will confirm an exact timeframe after a survey, since every property and heating system is slightly different.
Semantic entities that affect this answer
The time a job takes depends on five things working together: the boiler type you’re installing, how much pipework and flue work is needed, whether the boiler location is changing, the age and condition of your existing system, and the property type (flat vs house, and how accessible the boiler is).
Can a New Boiler Be Installed in One Day?
Yes — a same-day boiler installation is realistic for most standard combi boiler swaps, where the new boiler goes in the exact spot the old one occupied and uses the existing pipework, flue and gas supply.
A typical one-day boiler replacement includes:
- Removing the old boiler
- Fitting the new boiler in the same position
- Reconnecting gas, water, electrics and the flue
- Commissioning and testing the system
- A demonstration of the new controls
If your installer needs to reroute pipework, move the flue, or upgrade your gas supply pipe, a same-day finish becomes less likely, and the job may run into a second day.
How Long Does a Combi Boiler Take to Install?
A combi boiler installation typically takes 4 to 8 hours when it’s replacing another combi boiler in the same location.
Combi boilers are the quickest type to install because they combine heating and hot water in one unit, with no separate hot water cylinder or cold water tank to remove or fit. If you’re replacing an old combi with a new combi in the same spot, most installers can complete the job, test it and hand it back to you within a single working day.
Installation time increases if:
- The new boiler is a different size or brand with different pipe connections
- The flue needs to be extended or repositioned
- Your gas pipe needs upgrading to meet the new boiler’s specification
- The boiler is being moved to a different wall or room
How Long Does a System or Regular Boiler Take to Install?
A system boiler replacement usually takes 6 to 8 hours, while a regular (conventional) boiler replacement typically takes a full day, because both involve more components than a combi.
System boilers heat water and store it in a separate cylinder, so installers need to check and reconnect the cylinder, expansion vessel and associated pipework alongside the boiler itself.
Regular boilers (also called conventional or heat-only boilers) have the most components — a cold water storage tank, a hot water cylinder, and often a feed-and-expansion tank in the loft — so replacing one takes longer even when nothing is being relocated.
| Boiler Type | Extra Components | Typical Time |
|---|---|---|
| Combi | None (all-in-one unit) | 4–6 hours |
| System | Hot water cylinder | 6–8 hours |
| Regular/conventional | Cylinder + cold water tank | 1 day |
How Long Does It Take to Convert to a Combi Boiler?
Converting to a combi boiler takes longer than a like-for-like swap: a regular-to-combi conversion usually takes 1.5 to 2 days, and a system-to-combi conversion can take up to 3 days.
A conversion isn’t just a boiler swap — it changes how your whole heating system works, so the job typically includes:
- Removing the old boiler, hot water cylinder, and any cold water storage tanks
- Capping off pipework that’s no longer needed
- Running new pipework to and from the combi boiler
- Making good any walls, floors, or airing cupboards affected by removed tanks
- Full system flush, commissioning and testing
Because more pipework and often some plastering or decorating touch-ups are involved, engineers usually schedule these jobs over two to three days rather than trying to complete everything in one visit.
How Long Does It Take to Move a Boiler?
Relocating a boiler to a new room, wall, or cupboard usually adds a day or more to the installation, bringing total installation time to 1 to 2 days.
Moving a boiler means running new gas, water and electrical connections to the new location, and often extending or rerouting the flue so it still terminates safely outside the property. In flats and terraced houses, flue routing can be the biggest factor in how long this takes, since the flue often needs to reach an external wall or roof.
Boiler relocation projects generally take longer when:
- The new location is further from existing gas and water supplies
- The flue route needs to change direction or length
- Pipework has to be hidden behind walls or under floors
- Building regulations require additional ventilation or access checks
What Can Make a Boiler Installation Take Longer?
Several factors can extend boiler installation time beyond the standard estimates, and it’s worth knowing them before you book a job.
- Changing boiler type — switching from a regular or system boiler to a combi (or vice versa) always adds time
- Relocating the boiler — new pipework and flue routing take longer than reconnecting in the same spot
- Old or non-standard pipework — older properties sometimes need pipework replaced or upgraded to current standards
- Flue complications — flues that need to be extended, rerouted, or fitted through an awkward wall
- Limited access — boilers in tight cupboards, lofts, or hard-to-reach spots slow down removal and fitting
- Gas supply upgrades — some new boilers need a larger gas pipe than the one already installed
- Unexpected issues — corroded pipework, asbestos in older properties, or damage found once the old boiler is removed
- Power flushing — flushing the heating system to remove sludge and debris can add 3–4 hours or a separate visit
How Long Will Your Heating and Hot Water Be Off?
Your heating and hot water are typically off for the duration of the installation — usually 4 to 8 hours for a same-day swap, or overnight if the job spans more than one day.
This is the practical question most homeowners actually want answered. Here’s what to expect:
- Same-day combi swap: heating and hot water are off from when the engineer starts until commissioning is complete, typically 4–8 hours
- Multi-day installations: heating and hot water are usually off overnight between visits, so plan around this if you have young children, elderly relatives, or need hot water for medical reasons
- Water supply: your mains cold water is briefly turned off at points during the job but isn’t usually off for the whole installation
- Electricity: only the circuit powering the boiler is isolated, not your whole property
If you’re particularly concerned about downtime — for example, installing in winter or with vulnerable household members — mention this when booking so your installer can plan the job to minimise disruption.
What Happens on Boiler Installation Day?
On installation day, a Gas Safe registered engineer removes your old boiler, fits and connects the new one, then commissions and tests the whole system before handing it back to you.
A typical installation day follows these steps:
- Arrival and walkthrough — the engineer confirms the job scope and protects flooring and work areas
- Isolating the system — gas, water and electricity to the boiler are turned off
- Removing the old boiler — including any associated pipework being replaced
- Fitting the new boiler — mounting the unit and connecting gas, water, electrics and the flue
- System flush (if needed) — clearing sludge and debris from radiators and pipework
- Commissioning — running the boiler through its full cycle to confirm safe, correct operation
- Testing and safety checks — checking for leaks, correct pressure, and safe flue operation
- Handover — the engineer explains the controls, provides paperwork (including a Benchmark checklist and Gas Safe certificate), and registers the boiler with the manufacturer for its warranty
How Should You Prepare for a New Boiler Installation?
Preparing your home before the engineer arrives helps the job start on time and reduces the chance of delays.
- Clear the area around your existing boiler so there’s room to work
- Move furniture, boxes, or belongings out of the airing cupboard or utility room if that’s where the boiler sits
- Make sure there’s clear access from your front door to the boiler’s location
- Let the engineer know in advance about pets, parking restrictions, or building access rules (common in flats)
- Decide where you’d like the new boiler if it’s being moved, and flag this before the survey
- Charge your phone or keep a portable charger handy if you work from home, since Wi-Fi routers plugged in near the boiler may need to be moved
Most installers will ask you to be present at the start and end of the job, even if you don’t need to stay home the entire time — check this with your engineer when booking.
How Long Does Boiler Installation Take in London?
Boiler installation times in London are similar to the national average — around 4–8 hours for a straightforward swap — but London properties can add time due to flat access, parking, and older building layouts.
A few London-specific factors worth knowing:
- Flats and converted properties often have boilers in kitchen cupboards or hallway cupboards with limited access, which can slow down removal and fitting
- Parking restrictions in many boroughs mean engineers need to arrange permits or loading bay access in advance, which is usually sorted before the job, not on the day
- Older housing stock — common in boroughs like Lambeth, Hackney, and Tower Hamlets — sometimes has non-standard pipework that needs extra attention
- New-build flats and modern conversions — common in areas like Wandsworth and Croydon — usually have straightforward, standardised setups that fit the typical 4–6 hour window
Whether you’re in Barnet, Bromley, Enfield, Hillingdon, or central London, the boiler type and complexity of the job matter far more than the borough itself when it comes to timing.
What Does Boiler Installation Cost in London?
Boiler installation costs in London typically range from around £1,800 to £3,500 for a straightforward combi swap, with conversions and relocations costing more due to the extra labour and materials involved.
Cost depends on the same factors that affect installation time: boiler type, brand, whether pipework or the flue needs changing, and whether you’re converting to a different system type. If you’d like an accurate figure for your property, the most reliable way is to book a free, no-obligation survey with a Gas Safe registered installer.
Frequently Asked Questions About Boiler Installation Time
How long does it normally take to install a new boiler?
Most straightforward boiler installations take between 4 and 8 hours and are completed within one working day. More complex jobs, such as conversions or relocations, can take 1 to 3 days.
Can a new boiler be installed in one day?
Yes, a like-for-like combi boiler swap in the same location can usually be completed and tested within one day, often in 4 to 6 hours.
How many hours does a boiler installation take?
A standard combi replacement takes roughly 4 to 6 hours. System and regular boiler replacements typically take 6 to 8 hours, or a full day.
How long does a combi boiler installation take?
A combi-to-combi swap in the same position usually takes 4 to 6 hours. If the boiler is moving location, expect 6 to 8 hours or longer.
How long does it take to convert to a combi boiler?
A regular-to-combi conversion generally takes 1.5 to 2 days, while a system-to-combi conversion can take up to 3 days, due to the extra pipework and tank removal involved.
Will I have heating and hot water during the installation?
No, your heating and hot water are switched off while the engineer works, typically for 4 to 8 hours on a same-day job, or overnight if the installation spans more than one day.
Do I need to stay home during boiler installation?
You should be present at the start and end of the job so the engineer can walk you through the work and demonstrate the new controls, though you don’t usually need to stay home the entire time. Confirm this with your installer when booking.
Does moving a boiler make installation take longer?
Yes, relocating a boiler to a new wall, room, or cupboard adds new pipework and flue routing, which typically extends the job to 1 to 2 days.
What can make boiler installation take longer than expected?
Changing boiler type, moving the boiler, old or non-standard pipework, flue complications, limited access, and unexpected issues found once the old boiler is removed can all extend installation time.
How long does boiler installation take in London specifically?
London installation times are broadly the same as the national average, though flats, parking restrictions, and older properties in some boroughs can add time compared to straightforward houses with easy access.
The Bottom Line
For most London homeowners, a new boiler installation means one day of disruption — a few hours without heating and hot water while a Gas Safe registered engineer swaps out the old unit. Conversions and relocations take longer, but a good installer will always confirm your exact timeframe after a survey, so you’re never left guessing.
If you’re ready to find out exactly how long your installation will take, book a free survey with a Gas Safe registered engineer for an accurate, no-obligation quote.