How Long Will I Be Without Heating When My Boiler Is Replaced?
What decides how long a new boiler takes to fit, what happens on the day, and how to make it easier if it's done in the colder months.
By Summit Plumbing & Heating Solutions
For a straightforward swap, where the new boiler is the same type and goes in the same place as the old one, most homes are without heating and hot water for one working day. The heating is usually back on by the evening. Bigger jobs, such as moving the boiler or changing from a system with tanks to a combi, usually take two or three days. Your installer should tell you which yours is before the work is booked.
This post explains what makes a replacement quick or slow, what happens on the day, how long you'll be without heat and hot water, and a few ways to make it easier if the work happens in winter.
Why a like-for-like swap is quickest
When a combi boiler is replaced with another combi boiler in the same spot, most of the surrounding pipework can stay in place. The pipes are already in the right position, the flue (the pipe that carries fumes outside) usually exits through the same hole, and the controls may only need updating. The work mainly involves removing the old boiler from the wall, fitting the new one and connecting it up.
Jobs that take longer
A replacement takes longer when more than the boiler itself is changing. The most common reasons are:
Moving the boiler, for example from a kitchen to a loft or utility room. New pipework, a new flue route and a new condensate pipe (the plastic pipe that carries waste water from the boiler to a drain) all add time.
Changing boiler type, such as going from a regular or system boiler with a hot water cylinder and loft tanks to a combi. Taking out the tanks and cylinder and reworking the pipes usually adds a day or more.
Upgrading the gas pipe. Modern boilers often need a larger gas supply than the old one did, so the pipe from the meter may need replacing.
Cleaning the system. If the radiators and pipes are full of sludge (a dark build-up of rust and dirt), they may need flushing before the new boiler goes on, so the dirt doesn't damage it.
Replacing radiators or controls at the same time.
One landlord who had a new boiler fitted in a rented home told us the work was done "whilst keeping things clean and tidy for my tenants over the 2 days". A good installer will tell you how many days to expect at the survey, and why.
What happens on the day
A typical boiler replacement follows the same steps:
The installer protects floors and the work area, then turns off the gas, water and power to the boiler.
The heating system is drained, and the old boiler is taken off the wall.
The new boiler is fitted, along with any new pipework, flue and condensate pipe.
A magnetic filter is fitted on the heating pipes to catch loose dirt before it reaches the boiler.
The system is refilled, a liquid called inhibitor is added to slow down corrosion, and the radiators are bled.
The boiler is commissioned, which means it's tested and set up to burn gas safely, and the controls are set.
The installer shows you how to use the boiler and controls, and gives you the paperwork.
How long you'll be without heating and hot water
On a one-day job, expect the heating and hot water to be off from the time the installer starts until the new boiler is commissioned, usually late afternoon. You'll still have cold water from the kitchen tap, and electric appliances such as the kettle work as normal.
On a two or three-day job, ask your installer whether the heating can be restored overnight. Sometimes it can, and sometimes, for example when the old boiler is coming out and the new one isn't connected yet, it can't. Knowing in advance lets you plan.
Making it easier in the colder months
A new boiler can be fitted at any time of year, but a little planning helps in winter:
Don't wait for a breakdown if you can help it. If your boiler is old and unreliable, replacing it on a planned date is far easier than waiting days with no heat after it fails.
Have a plan for the day. A portable electric heater for one room, extra layers, and somewhere to shower if the job runs over a day all help.
Think about who's at home. If you have young children, someone elderly or pets in the house, mention it so the work can be planned around them.
Clear the way. Clear space around the boiler, under the sink and in any loft or cupboard the installer needs, so they can start promptly.
The paperwork after it's fitted
Once the boiler is in, the installer should register the manufacturer's warranty for you, fill in the boiler's commissioning checklist (often called the Benchmark), and notify Gas Safe Register. Gas Safe Register then sends you a Building Regulations compliance certificate by post, usually within a few weeks. Keep it with your house documents, as you'll need it if you sell.
Most warranties also depend on a yearly boiler service, so it's worth putting a date in the diary for a year's time.
Getting a clear timescale
Summit Plumbing & Heating Solutions is Gas Safe registered and a Vaillant Advance installer, and fits boilers from Vaillant, Worcester Bosch and Ideal. Every installation includes a magnetic filter, and where a system needs cleaning we can include a rapid flush. We'll tell you at the survey how long your job will take and how long you'll be without heating. Find out more about our boiler installation service and book a survey.
