How New Boilers Are Installed, Step-by-Step

If your current boiler is on its last legs, you might be wondering what it takes to get a new one up and running. After all, replacing your boiler is a big job, so it’s only natural to be curious about what will be happening in your home.

Greenstar have installed boilers in homes all across the South, so we know a thing or two about the steps involved. In this guide, we’ll walk you through the entire process – from the initial survey to the final boiler test – so you know exactly what to expect.

1. Survey and Quotation

First things first, a Gas Safe registered engineer will visit your home for an initial assessment. They’ll talk with you to understand your hot water and heating needs, then survey the property to assess its layout, see how many radiators you have, and determine the best placement for the boiler.

They’ll then walk you through different boiler types – combi, system, or regular – and recommend models that would be a good fit for your home. They’ll be happy to follow your preferences, but if you’re unsure, they can offer some expert advice too.

Once everything’s checked out, they’ll give you a clear quote that breaks down all the costs for both the equipment and the work itself.

2. Removing the Old Boiler

You can skip the next two sections if your new boiler’s going in a new build.

After you approve the quote, the engineer will schedule a separate visit to remove your old boiler. Here’s what they’ll do:

Turn off the gas supply at the metre and isolate the boiler electrically.
Locate and close the valves on the cold water feed and heating return pipes connected to the boiler.
Open a drain cock on the boiler or system to drain any remaining water, which will prevent leaks and make the boiler lighter to move.
Disconnect the gas pipe (for gas boilers) and any electrical wires once drained.
Use wrenches or pipe cutters to disconnect the pipes that connect the boiler to your central heating system.
Dismantle the flue pipe that vents exhaust gases (depending on the type of boiler you have).
Unscrew any brackets or bolts holding the boiler in place.
Assess the size and weight of the disconnected boiler. They might use lifting equipment or manpower to safely remove the unit and dispose of it responsibly.

3. System Flush

Before fitting your new boiler, your engineer will probably offer to carry out a system flush first. This is highly recommended – over the years, central heating systems can build up sludge and gunk. A power flush or chemical clean can clear this out, making sure your new boiler runs smoothly and efficiently right from the start.

4. Installing the New Boiler

Now we’re onto the exciting part: installing your new boiler! The engineer’s exact steps might vary depending on your system, but here’s a general idea of the elements they’ll work on:

Pipework

The engineer will usually begin by connecting the new boiler to the existing pipework for central heating and hot water (if applicable). Depending on the configuration of your system, this might involve modifications to the existing pipes, such as cutting, soldering, or adding new sections.

Flue

The flue is a pipe that vents the exhaust gases produced by the boiler safely outside the home. The engineer will connect the flue system securely to the boiler, making sure it’s properly sized and positioned first.

Gas Supply (if Applicable)

If your boiler is gas-powered, the engineer will connect it safely to your gas line. This includes checking for leaks and making sure everything meets strict gas safety regulations.

Electrical Supply

The engineer will connect the boiler to the electrical supply, making sure the wiring meets all electrical safety regulations. This may involve installing additional electrical circuits or outlets if needed.

Thermostats

In most cases, the existing thermostat can likely be reused with the new boiler, especially if it’s a like-for-like replacement and uses the same wiring system.

However, if you’re upgrading to a more advanced thermostat type (e.g. programmable or smart thermostat), the engineer might need to install a new one and wire it to the boiler’s electrical controls.

5. Testing the System

After everything’s connected, the engineer will give things a thorough once-over to make sure everything is safe and performing as it should. Here’s what they’ll typically do:

Visually inspect the system for any leaks, loose connections, or anything that looks out of place (like the flue being in the wrong position).
Test the gas pressure, flue gas, and electrical connections to make sure everything is working safely.
(Optional) Use an air pressure test to detect any leaks in the system before filling it with water.
Pressurise the water-filled system to a specific level and keep an eye on it for any pressure drops.
Make sure the thermostat and any control panels are working properly by giving them a test run.
Turn on the hot water tap to see if the temperature and flow rate are as expected.
Test the heating system and see if the radiators warm up sufficiently.
Commission the boiler, which basically means setting the controls and making sure it’s running at its best.

6. Handover and Support

Once your engineer is satisfied with how safe and efficient your new system is, they’ll hand over all the manuals and warranty information you’ll need, and show you how to use the new boiler controls and thermostats. They might also suggest scheduling a follow-up visit and offer to set up a long-term servicing plan.

Need a New Boiler Installed? Trust Greenstar for a Service You Can Count On

Thinking about replacing your boiler? Greenstar can help! With over 30 years of experience in installing boilers in homes across the South, our Gas Safe registered engineers are fully qualified to get the job done right.

Here’s why you should choose us:

We can install a wide range of boilers, from combi to system boilers, in properties of all shapes and sizes.
All of our engineers are highly trained and qualified to work on boiler systems.
We usually complete installations within 24 hours.
Our budget-friendly financing option lets you spread the cost out over up to 10 years. We provide extended guarantees on Worcester Bosch boilers, giving you peace of mind for up to 12 years.
We also provide boiler servicing and emergency repairs, making us a complete one-stop-shop for all your boiler needs.
We’ve received hundreds of glowing reviews on Checkatrade and Google.
After installation, your first boiler service with us will be totally free!