How Long Does It Take to Install a Boiler? One Day to a Week
A like-for-like boiler swap usually takes one day. Moving the boiler or changing the system type takes 1 to 2 days, and a full new heating system can take a week. What happens on each day and what slows it down.
A like-for-like boiler replacement, where the new boiler goes in the same place and is the same type as the old one, usually takes 4 to 6 hours and is finished in one day. Moving the boiler, changing from a regular or system boiler to a combi, or removing a back boiler usually takes 1 to 2 days. Installing a complete new central heating system with pipework and radiators can take several days to a week, depending on the size of the property.
Key Takeaways
- Like-for-like swap: about 4 to 6 hours, normally one day, with heating and hot water back the same evening.
- Moving the boiler or converting the system type: usually 1 to 2 days.
- A full new heating system with radiators and pipework: several days to a week.
- Cleaning the old system before the new boiler goes on is part of the job and adds time, but protects the new boiler and its warranty.
- The engineer must register the installation with building control; you get a compliance certificate afterwards.
Most boiler installations take one day. If the new boiler is the same type as the old one and goes in the same place, the fitting itself is usually 4 to 6 hours, and you have heating and hot water back the same evening. The job gets longer when the boiler moves, when the system type changes (for example from a tank-fed system to a combi), or when radiators and pipework are being replaced too. Those jobs typically take 1 to 2 days, and a full new heating system can take a week.
For the price side of the same decision, see our boiler installation cost guide. If you are still deciding which kind of boiler to fit, our combi vs system boiler comparison covers which suits which home.
Boiler installation times by type of job
| Job | Typical time | Why |
|---|---|---|
| Like-for-like combi swap, same position | 4 to 6 hours (1 day) | Existing gas, water, flue route and condensate can usually be reused or adapted |
| Like-for-like system or regular boiler | 1 day | Similar to a combi swap, with extra controls and cylinder connections to check |
| Moving the boiler to a new position | 1 to 2 days | New gas run, new flue hole, new condensate route and pipework alterations |
| Regular or system boiler to combi conversion | 1 to 2 days | Cylinder and loft tanks removed, redundant pipes capped, mains connections made |
| Back boiler removal and new boiler | 1 to 2 days | Old boiler and fire removed, chimney made safe, new boiler fitted elsewhere |
| New system boiler with new unvented cylinder | 2 to 3 days | Cylinder installation, discharge pipework and controls on top of the boiler |
| Full new central heating system | Several days to a week | Pipework and radiators through the house, floorboards up, then boiler and controls |
These times assume a team of one or two engineers and no nasty surprises. A big house or a hard-to-reach boiler position adds time. Two engineers on site can shorten a two-day job.
What happens on installation day
Protect the house and isolate
Dust sheets go down, the gas, water and electrics to the boiler are isolated, and the engineers check the plan against the survey.
Drain down and remove the old boiler
The heating system is drained, the old boiler and flue are taken off, and any redundant parts are removed. On a conversion this is when the cylinder and loft tanks come out.
Clean the system
The heating system is cleaned before the new boiler is connected, so old sludge does not go straight into it. Depending on the condition of the system this ranges from a chemical cleanse to a full power flush. Most manufacturers need this done to honour the warranty.
Fit the boiler, flue and pipework
The new boiler is hung, the flue is fitted, and the gas, water, heating and condensate pipes are connected. A magnetic system filter is usually fitted on the return pipe at this stage.
Fill, test and commission
The system is filled, bled and treated with inhibitor. The gas is tested for tightness, the boiler is fired up, and the engineer checks the combustion and sets it up to the manufacturer's figures.
Controls and handover
The thermostat and controls are connected and set. The engineer shows you how to use them, fills in the benchmark checklist and explains how to register the warranty.
What makes a boiler installation take longer
- A dirty system. Heavy sludge means a longer clean. A full power flush on its own can take most of a day; our guide on how long a power flush takes explains why.
- An undersized gas pipe. Modern combis often need a bigger gas supply than the old boiler. Upgrading the pipe from the meter can add a few hours.
- Flue changes. A new flue route, a vertical flue through the roof, or a flue that needs a plume kit to keep it away from windows and neighbours all add time.
- Condensate drainage. Condensing boilers produce water that needs a proper drain. If there is no nearby waste pipe, a new run or a condensate pump is needed.
- Access. Loft installations, tight cupboards and upper-floor flats with no parking or lift all slow things down in London.
- Problems found on the day. A leaking radiator valve, corroded pipework or a seized isolation valve may need fixing before the new boiler can be commissioned.
How long will you be without heating and hot water?
On a one-day swap, usually from mid-morning until late afternoon. The water supply to the rest of the house is normally only off for part of that time, so you can still use the toilet and cold taps for most of the day.
On a conversion or a relocation, you may be without heating and hot water overnight. If anyone in the house is elderly, unwell or has a baby, tell the installer at the survey. It can sometimes be arranged so the old system is kept running until the second day, or so the new boiler is working by the end of day one with the tidying-up done later.
Before the installation day
The installation day is only part of the timeline. Before it there is a survey, where an engineer checks the gas supply, the flue route, the water pressure and flow, the size of the house and how you use hot water, then recommends a boiler and gives you a quote. Once you accept, the date depends on parts and diary space. Autumn and winter are the busiest months, so if your boiler is old but still working, planning the swap in summer usually gets you more choice of dates. Our guide on how long boilers last can help you judge whether it is time.
On the day, clear the area around the boiler, the route to it, and the loft hatch if the tanks or flue are up there. Make sure the engineers can reach the gas meter and the stopcock.
After the installation
The engineer has to register the new boiler with building control through the Gas Safe Register. You should then receive a Building Regulations Compliance Certificate in the post. Keep it with the benchmark checklist, because you will need both if you sell the house or make a warranty claim.
Register the manufacturer's warranty straight away if the installer has not done it for you, and book the first boiler service for about a year after fitting. Most warranties depend on that service being done on time.
Want a clear timescale for your new boiler?
Tell us what boiler you have now, where it is and what you want to change. We'll survey the property and confirm how long the job will take before anything is booked.
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Frequently Asked Questions
How long does it take to install a new boiler?
A like-for-like replacement in the same position usually takes 4 to 6 hours and is done in one day. Moving the boiler or changing the system type usually takes 1 to 2 days, and a full new central heating system can take several days to a week.
How long does it take to convert to a combi boiler?
Converting from a regular or system boiler to a combi usually takes 1 to 2 days. The extra time goes on removing the hot water cylinder and loft tanks, capping off redundant pipes and connecting the combi to the mains supply.
Will I have heating and hot water on the night of the installation?
On a one-day like-for-like swap, yes in nearly all cases. On a two-day job you may be without heating and hot water overnight, so ask the installer to plan the work so you have hot water on the first evening where possible.
Do I need to be home during a boiler installation?
Someone needs to let the engineers in, be reachable during the day, and be there at the end so the engineer can show you the controls and hand over the paperwork. You do not need to watch the work.
How soon can a new boiler be fitted?
It depends on the survey, parts availability and the time of year. A like-for-like swap is often possible within days of accepting a quote. Autumn and winter are the busiest months, so booking in summer usually means more choice of dates.
Sources and further reading
Source links checked 27 September 2026. Scheme rules and manufacturer instructions can change; use the current official guidance for your account or exact appliance.