How Long Does It Take to Replace a Boiler in a House?

Replacing a boiler isn’t like swapping out a lightbulb. It’s a major job that affects your home’s comfort, safety, and energy bills. If you’re wondering how long it takes to replace a boiler in a house, the short answer is: one to three days for most homes in New Zealand. But that number can shift depending on your setup, the type of boiler, and what’s involved behind the walls.

What Happens on Day One: Removal and Prep

Most boiler replacements start with removing the old unit. This isn’t just unscrewing a few bolts. The old boiler is usually bolted to the wall, connected to gas and water pipes, and wired into your electrical system. A qualified technician will shut off the gas supply, drain the heating system, disconnect the flue, and carefully remove the unit. If your old boiler was installed in the 1990s or earlier, you might find rusted pipes, outdated fittings, or even asbestos insulation around the pipes-common in older homes in Wellington and other parts of New Zealand. That adds time.

Once the old boiler is out, the team checks the condition of the pipework, gas line, and flue. If the existing pipes are in good shape and the gas supply is up to current code, they’ll reuse them. But if the pipes are corroded, too small, or made of lead, they’ll need replacing. Same goes for the flue. Modern condensing boilers need a dedicated condensate pipe that drains into a sink or outdoor drain. If your home doesn’t have one, a new line has to be run. These surprises can add a few hours-or even push the job into a second day.

Day Two: Installation and Connection

This is where the new boiler comes in. Most modern boilers in New Zealand are condensing models, which are more efficient and require a condensate drain. The installer will mount the new unit, connect the gas line (using a certified gas fitter), attach the water pipes, and hook up the electrical supply. The flue is then secured, often going through an outside wall or roof. In apartments or homes with shared flues, this can get complicated.

The boiler also needs to be programmed and tested. This includes filling the system with water, bleeding the radiators, checking for leaks, and setting the thermostat and timer. The installer will run the boiler for at least 30 minutes to make sure everything heats up properly and there are no pressure drops or unusual noises. If your home has a combi boiler, they’ll also test the hot water flow rate. A good system should deliver hot water within seconds of turning on a tap.

Day Three: Final Checks and Cleanup

If everything went smoothly, the job might finish on day two. But many installers prefer to come back on day three for a final inspection. This includes checking the boiler’s pressure (it should be between 1 and 1.5 bar), verifying the flue is clear, and making sure the condensate pipe doesn’t freeze in winter (a real concern in Wellington’s damp climate). They’ll also give you a boiler certificate-required by law in New Zealand under the Gas Safety Regulations-and register the installation with the manufacturer for warranty purposes.

You’ll also get a walkthrough. The installer will show you how to reset the boiler if it cuts out, how to top up the pressure, and where the isolation valves are. If you’ve got a smart thermostat, they’ll help you pair it with the boiler. Most modern boilers have digital displays with error codes. Knowing what those mean can save you a service call later.

What Can Slow Things Down?

Not every boiler replacement follows the three-day timeline. Here’s what can delay things:

• Old plumbing: Homes built before 1980 often have copper or iron pipes that don’t connect easily to modern fittings. Replacing these adds time and cost.
• Location: If your boiler is in a cramped cupboard, under stairs, or in a basement, it’s harder to get the new unit in and out. Some installers charge extra for difficult access.
• Flue routing: If your home doesn’t have a suitable wall for the flue, or if the nearest exterior wall is far away, the installer may need to drill through multiple walls or even the roof. This requires more labor and possibly scaffolding.
• System upgrades: If you’re switching from a regular boiler to a combi, you might need to remove the hot water tank. That means clearing out a whole room, patching walls, and repainting.
• Weather: In Wellington, winter storms can delay outdoor work. If the flue needs to be installed in rain or high wind, the team might reschedule for safety.

How Long Does It Take to Get a New Boiler Installed? (The Waiting Game)

The actual installation time is just one part of the puzzle. The bigger delay is often getting the job scheduled. In New Zealand, demand for boiler replacements has risen since 2023, especially after the government’s Warm Home Initiative pushed homeowners to upgrade old, inefficient units. Many plumbers are booked 2-4 weeks out. If you need emergency heat during winter, you might pay extra for a same-day service, but that’s not always possible.

You’ll also need to wait for the boiler to arrive. Most boilers are ordered from suppliers in Auckland or Christchurch. Delivery can take 3-7 days. Some installers keep popular models in stock, but if you want a specific brand like Worcester Bosch or Vaillant, you might wait longer.

What You Should Do Before Replacement

To keep things smooth, prepare ahead:

• Clear the area around your boiler. Move furniture, rugs, and storage boxes. Installers need at least 1 meter of space.
• Turn off the power and gas supply if you can. It’s not required, but it helps.
• Ask for a written quote that includes removal, disposal, labor, parts, and flue work. Some quotes don’t include the condensate pipe or new radiators.
• Check if your installer is registered with the Gas Safe Register (New Zealand equivalent: Gasfitters Register under the Gas Safety Regulations).
• Ask if they handle disposal. Old boilers aren’t just trash-they contain metals and sometimes refrigerants. Reputable installers take them to certified recycling centers.

What’s the Difference Between Replacement and Repair?

It’s worth noting: if your boiler is leaking, making strange noises, or not heating properly, it might just need a repair. Most repairs-like replacing a pump, thermostat, or pressure valve-take a few hours. But if your boiler is over 10 years old and has had multiple repairs, replacement is usually smarter. A 15-year-old boiler can cost 30% more to run than a new one. In Wellington, where winters are cold and damp, that adds up fast.

Real-World Example: A Wellington Home

Last winter, a family in Miramar replaced their 1998 Vaillant boiler. The old unit was in a tiny cupboard under the stairs. The pipes were rusted, the flue went through the roof, and the condensate pipe drained into a sink that was too far away. The installers spent one day removing the old unit and clearing debris. Day two was spent installing the new Worcester Bosch Greenstar 4000, rerouting the condensate line, and testing everything. Day three was for final checks and paperwork. Total time: 3 days. Cost: $5,800 including disposal and flue work. They now save $40 a month on heating bills.

Final Thoughts

Replacing a boiler isn’t a weekend DIY project. It’s a professional job that needs gas certification, plumbing skills, and electrical knowledge. Most homes get it done in 1-3 days. But if your home is old, your layout is tricky, or you’re replacing more than just the boiler, expect delays. The key is planning ahead, choosing a registered installer, and asking the right questions before signing any contract. A well-installed boiler can last 15 years or more-and keep your home warm through Wellington winters without breaking the bank.