Why I Asked: How Long Does It Take to Fit a New Boiler?

When my old boiler started giving up during the colder months, I knew it was time for a replacement.

But one of the first questions I had was a practical one: how long does it take to fit a new boiler? I wasn’t sure if I’d need to take time off work or plan for days without hot water tank or heating.

After going through the process myself, I realised there’s more to it than just the boiler unit. The type of boiler, the complexity of the job, and even where the boiler is located all play a role.

In this guide, I’ll share exactly what I learned from my installation—so you can be better prepared than I was.

How Long Did My Boiler Installation Actually Take?

For me, the process took just under two days.

I had a conventional boiler replaced with a combi boiler, and because it involved updating the pipework and removing an old water tank, it wasn’t a simple swap.

If you’re having a like-for-like replacement—say, a combi boiler replaced with another combi in the same place—it’s often done in a single day.

But anything beyond that, especially if you’re upgrading or relocating the boiler, will take longer.

What Factors Affect the Time to Install a New Boiler?

I learned quickly that no two installations are exactly the same.

Here are the main elements that influenced how long mine took:

Type of Boiler Being Installed

Swapping a combi for a combi is actually the speedest route.

But switching from a system or regular boiler to a combi (like I did) adds time because it requires extra plumbing and removal of old components.

Location of the Boiler

If the new boiler goes in the same spot as the old one, that saves a lot of time.

But if you move it—say, from the kitchen to the loft or airing cupboard—you’re looking at added hours or even an extra day.

Age and Condition of the Existing System

My property had an older heating system, which meant some of the pipework needed replacing.

The engineer also recommended a system flush to clear out years of sludge. With all of that additionally added to the fitting time.

Whether You Need Extra Work

In my case, I opted to install a smart thermostat and also had some radiator valves replaced. Optional upgrades like this extend the job slightly but can be worthwhile long-term.

How Long Does It Take to Fit Each Type of Boiler?

Here’s a breakdown of typical timelines based on my research and personal experience:

Type of Installation	Estimated Time
Combi to Combi (same location)	1 day
System to Combi (conversion)	2 days
Regular to Combi (full upgrade)	2–3 days
Relocation or major pipework changes	2–3 days or more

If everything goes smoothly, even complex installations can be wrapped up in two days. But it’s always wise to allow for an extra half-day in case of unexpected issues.

What Happens During Boiler Installation?

This was something I didn’t fully understand until I watched it happen. Here’s a general step-by-step look at how the boiler fitting process unfolded for me:

1. Initial inspection and safety checks
2. Draining the system and removing the old boiler
   
3. Installing the new unit, flue, and any pipework
   
4. Connecting to gas, water, and electricity supplies
   
5. Carrying out a system flush, if required
   
6. Testing the boiler and heating system
   
7. Registering the boiler for warranty and Gas Safe compliance

It was helpful to know this in advance so I wasn’t left wondering what was happening at each stage.

Can I Speed Up the Boiler Installation Process?

I found that preparation goes a long way. Here are a few things I did to make life easier for the engineer—and save time:

My Boiler Prep Tips:

• Cleared the space around the boiler beforehand
  
• Made sure someone was home to provide access
  
• Shared the model I’d chosen in advance
  
• Asked about any extra work (e.g., pipe upgrades, thermostat fitting) during the survey
  

A good engineer will work efficiently, but making the job easier for them can shave off unnecessary delays.

Do I Need to Be Home for the Whole Installation?

I stayed in for most of the day, mainly to be on hand in case any decisions had to be made.

However, for large parts of the install—like flushing the system or fitting the flue—I wasn’t needed.

If you’re comfortable, you can step out for errands, but I’d recommend being there at the beginning and end, at the very least.

Is Boiler Fitting Messy or Disruptive?

This was one of my concerns, especially since the boiler is in the kitchen. Thankfully, the disruption was minimal. The engineer used dust sheets and cleaned up thoroughly.

That said, there was a bit of noise from drilling and water draining, and I had no heating or hot water for a day. If you’re sensitive to that, it’s worth planning accordingly.

What is the Best Time of Year to Fit a New Boiler?

I chose to have it installed in late summer, and I’m glad I did.

Heating engineers tend to be less busy in the warmer months, which meant I got quicker booking and more flexibility with dates.

Winter is when most breakdowns happen, so if you can, it’s a smart move to plan a boiler upgrade before the cold sets in.

Final Thoughts: What I Learned from My Boiler Installation

So, how long does it take to fit a new boiler? In my case, it was just under two days—but that included a system conversion, some extra upgrades, and a location change.

A simple like-for-like replacement could easily be done in a single day.

The key takeaway is to understand the specifics of your setup. By asking questions during the quote stage and preparing your home in advance, you can make the whole process smoother and possibly even faster.

If you’re thinking about replacing your boiler, give yourself a buffer of time—but know that a well-planned install doesn’t have to be a major disruption.