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

Replacing a boiler in your house isn’t something you can rush. It’s not like swapping out a light bulb. But it’s also not a multi-week project either. If you’re asking how long it takes to replace a boiler, the short answer is: one to two days for most homes in Auckland. But that’s just the start. What happens before and after matters just as much.

What Happens on Day One

Most boiler replacements start early in the morning. The engineer arrives with the new unit, tools, and parts. First thing they do is turn off the gas and electricity. Then they drain the old system. This isn’t just about shutting off a valve-it’s about making sure every drop of water is out of the pipes, radiators, and the boiler itself. In older homes, this can take longer. Rusty pipes, trapped air, or blocked drains can add extra time.

Next, they remove the old boiler. If it’s a combi boiler, they’ll likely find it tucked under the kitchen sink or in a utility cupboard. In older houses, you might see a big, clunky system boiler with a separate hot water tank. Removing it means disconnecting gas lines, water pipes, flue pipes, and electrical wires. Sometimes, the old boiler is bolted to the wall. That takes a drill. Other times, it’s just sitting there, held by decades of rust and neglect. That takes patience.

Once the old unit is out, they check the condition of the surrounding area. Is the wall strong enough to hold the new boiler? Are the gas and water pipes in good shape? Are the flue and condensate pipes clear? If the flue pipe is cracked or the condensate pipe is frozen (yes, that happens in Auckland winters), those issues get fixed on the spot. That’s why some jobs take longer than others.

Installing the New Boiler

The new boiler is unpacked and positioned. Most modern boilers are wall-mounted and lighter than the old ones. But they still need to be level, secure, and aligned with the flue and pipe connections. The engineer will use a spirit level, pipe cutters, and a gas leak detector. They’ll connect the gas line first-always with a pressure test. Then the water pipes. Then the electrical. Each connection gets checked twice.

If you’re switching from a system boiler to a combi, or vice versa, the plumbing changes. A combi doesn’t need a hot water tank, so they’ll cap off or remove those pipes. That means extra work. If you’re upgrading to a higher-output boiler, they might need to upgrade the gas supply line. That’s a job for the gas network provider, not the installer. And that can add a day or two to the timeline.

Testing and Commissioning

After everything’s connected, the system is filled with water. The engineer turns on the gas and powers up the boiler. They’ll check for leaks, airlocks, and proper pressure. Then they’ll run the heating and hot water. You’ll see the radiators heat up. You’ll turn on the tap and wait for hot water. If it doesn’t come on right away, they’ll bleed the system. That’s normal.

They’ll also program the thermostat and timer. If you’ve got a smart thermostat, they’ll pair it with the boiler. They’ll show you how to reset it if it locks out. They’ll explain the warranty and what to do if the display shows an error code. This part takes about an hour. But it’s the most important. A boiler that’s installed wrong can be dangerous.

What Can Delay the Job

Not every boiler replacement goes smoothly. Here’s what can throw things off:

• Old or blocked flue - If your flue is corroded or too small for the new boiler, you’ll need a new one. That’s extra cost and time.
• Condensate pipe freeze - In winter, the pipe that drains condensate can freeze. They’ll need to thaw it or reroute it.
• Gas supply upgrade - If your house has an old 15mm gas line and you’re installing a 35kW boiler, you’ll need a 22mm line. That requires approval and a separate technician.
• Unforeseen wall damage - Sometimes, removing the old boiler reveals rot, damp, or electrical hazards. That needs fixing before the new one goes in.
• Waiting for parts - Rare models or discontinued units might need ordering. That can add a day or two.

How to Speed Things Up

You can help make the process faster:

• Clear the space - Move furniture, boxes, and rugs away from the boiler area. Give them at least 1.5 meters of access.
• Have the old boiler’s details ready - Know the make, model, and serial number. If you have the manual, hand it over.
• Decide on the new boiler type - Don’t wait until the day of install to ask, “Should I get a combi or system boiler?” Talk to your installer ahead of time.
• Check your flue and condensate route - If you know where the flue goes (usually out the side wall or roof), point it out. If the condensate pipe runs to the drain under the sink, make sure it’s accessible.

What to Expect After Installation

The day after installation, you might notice a few things:

• The boiler might make a slight gurgling noise as air works its way out of the pipes.
• One or two radiators might be cold at the top. That’s air. Just bleed them.
• The boiler might cycle on and off more often at first. That’s normal as it learns your home’s heating pattern.

Your installer should leave you with a commissioning certificate. That’s proof the job was done safely and to code. Keep it. You’ll need it if you ever sell your house. Also, register the boiler with the manufacturer. Most warranties are void if you don’t.

Boiler Replacement Timelines in NZ Homes

In Auckland, most homes get their boilers replaced in one day. That’s true for flats, townhouses, and standard family homes. But larger houses with multiple zones, underfloor heating, or complex pipework might take two full days. If you’re replacing a boiler in a 1950s villa with original cast iron pipes, expect delays. The same goes for homes with no access to the outside wall for the flue.

The average time for a straightforward boiler swap in a modern home: 6 to 8 hours. That includes removal, installation, testing, and cleanup.

When to Call a Professional

Don’t try to replace your boiler yourself. Gas work is illegal without a licensed gas fitter in New Zealand. Even if you’re handy, the risks aren’t worth it. A gas leak can kill. A faulty flue can fill your home with carbon monoxide. And if something goes wrong, your insurance won’t pay out.

Always use a registered gas fitter. You can check their registration on the Gas Register website. Look for someone who specializes in boiler replacements-not just general plumbing.

How Often Should You Replace Your Boiler?

Most boilers last 10 to 15 years. If yours is over 12 years old and you’re seeing:

• More frequent repairs
• Higher gas bills
• Strange noises or smells
• Yellow flames instead of blue

…it’s time to replace it. Waiting too long can lead to a breakdown in winter. And that’s when replacement quotes go up and installers get booked out.

Next Steps

If you’re thinking about replacing your boiler, don’t wait until it breaks. Book a free assessment with a registered gas fitter. They’ll check your system, explain your options, and give you a fixed quote. Most offer no-obligation quotes. Use that time to ask questions about efficiency, warranty, and future-proofing.

Don’t be fooled by the cheapest quote. The lowest price often means the installer is cutting corners on safety or skipping proper testing. A boiler is one of the most important systems in your home. Get it done right the first time.