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Changing From Conventional Boiler To Combi Guide


“Change is the only thing that’s constant.” That saying is particularly true as far as technology is concerned.

Combi Boilers are currently the most trending boilers in the market. Many homeowners, including you, are considering the change, and it’s not hard to understand why.

Are you still having doubts? All us to explain all we can about changing from conventional boilers to combi boilers. We’ll be discussing some of the most important factors like whether or not they’re worth it and, of course, the costs you’ll incur.

Factors to consider before changing from a conventional boiler to a combi boiler

The unit’s specifications

Indeed, combi boilers come in many models and types. It’s up to you and your team of engineers to consider what works best with your property.

The first most important factor is the boiler’s Kilowatt Output. The boiler needs to be strong enough to serve the desired building.

Next, pay attention to the boiler’s hot water flow rate. It needs to be sufficient enough to serve the entire house. Flow rate reads in Litres Per Minute (LPM). Some boilers record higher values than others. If you have a big house, the higher the numbers, the better.

To get it right, consult with your engineers and come up with the most accurate water requirement for your property. Generally, each shower needs about 5 LPM. On the other hand, baths require 8 LPM per unit.

Home decor

Depending on the scale and size of your property, changing from a conventional to a combi boiler might drastically affect your home’s space. Since a combi boiler system is more conservative, there might be some awkward blank space after removing the storage and attic tanks.

Ideally, we advise property owners to change their boiler systems before doing serious cosmetic or decorative work. That way, you’ll not have to worry about filling leftover spaces.

Changing From Conventional Boiler To Combi Guide

We’re not going to kid you. Combi boiler instalment/replacement can be costly and time-consuming. Depending on your situation, it can take anywhere from a few days to a whole week.

Can you change from a conventional to a combi boiler by yourself?

No, DIY skills can’t prepare you for the difficult and dangerous task that awaits. It involves more than unplugging and plugging boilers. You’ll also have to consider the pipework.

If you’re uneducated, the task will be overwhelming and risky. A poorly installed boiler can easily turn a happy home into a hazard. On top of that, you’ll face hefty fines and possible jail time if they discover that your boiler was installed without the help of a certified gas engineer.

It takes 5 years of strict training to become a certified gas engineer. It takes an additional 5 years of experience before you can comfortably handle an installation on your own. That’s how delicate it is.

Below are the general steps that gas engineers are likely to follow when installing a combi boiler.

  • They first drain all of your system’s hot water.
  • Next, they uninstall your existing conventional boiler.
  • They then unplug all of your existing thermostats. This step isn’t always necessary (especially if you’ve recently installed modern ones). However, take note that new thermostats will increase the cost.
  • Most importantly, they’ll get rid of the “old” conventional attic tanks. Also, you are advised to allow them to inspect your pipework. There might be some faults that might worsen after installing the new combi boiler.
  • Now, they’ll install the new combi boiler and required pipework.
  • Soon after, they’ll do a power flush on the whole boiler system. On the same day, they might also install the magnetic filters
  • They’ll then install new thermostats. We advise you to go for smart thermostats that will help boost your energy-saving efforts.
  • Finally, they’ll run a couple of tests to make sure all is well. Additionally, expect the engineers to give you some tips on how you should use and maintain your new combi boiler system.

How much does it cost to install/change a combi boiler?

As you might have expected, the total cost will vary depending on the circumstance.

Most of the time, the cost is determined by the system’s complexity. A more complex system will cost more to replace and install than a simpler one.

Likewise, combi boiler replacement/installation will cost less for a smaller house than a larger one.

Contrary to popular belief, it’s the installation/replacement that accounts for a huge chunk of the cost, not the combi boiler itself. Nonetheless, the situation might change if you opt for high-end or flagship combi boilers.

On average, property owners should expect to spend somewhere between £2000 to £2500.

Of course, that’s just a rough estimate. We advise you to request a combi boiler quote for a more accurate estimation.

Below are some combi boiler conversions that will give you a rough estimate of the amount of time and money it will cost you.

  • Regular boiler to combi boiler– It will cost you around £2200 to £2500. The replacement should take around 2 days to complete.
  • Back boiler to combi boiler– It will cost you around £2400 to £3000. The replacement should take around 2 to 3 days to complete.
  • System boiler to combi boiler– It will cost you around £2000 to £2450. The replacement should take around 2 days to complete.
  • “Old” combi boiler to “new” combi boiler– It will cost you around £2200 to £2500. The replacement should take around 2 days to complete.

Benefits of combi boilers

Below are some of the advantages that come with the “modern” combi boilers.

They are highly efficient and help save money

Did you know that a combi boiler can help you save up to 40% on electricity bills?

By changing to combi boilers, most homeowners will save up to £310 per year. On top of that, a combi boiler installation will further boost your home’s value. It’s a nice long-term investment.

Chances are, your conventional boiler has seen better days and is currently operating at 50% efficiency. On the other hand, most mid-range to high-end boilers can maintain 90% efficiency for years.

Thanks to Condensate Technology, combi boilers are on a whole other level as far as efficiency is concerned.

Believe it or not, there are some combi boilers with 98% energy efficiency.

Conventional boilers usually heat water twice a day, in the morning and evening. However, most of the time, homeowners only use a fraction of that water, and the rest ends up cooling in the storage tanks. That’s a waste.

On the other hand, combi boilers produce hot water on demand. Therefore, no energy is wasted.

They help save indoor space

Conventional boilers need attic tanks to store heated water. Unfortunately, these tanks take up home space. On the other hand, combi boilers produce water on demand and don’t require storage tanks. Also, combi boilers require less pipework than conventional boilers. They are the perfect central heating solutions for flats and the trendy “tiny homes.”

Finally, we even have compact combi boilers that can fit in kitchen cabinets.

Combi boilers are more durable

As mentioned earlier, combi boilers require fewer components like pipework. Therefore, they suffer less from corrosion and thermal stress. On top of that, they are equipped with modern technology.

With proper and affordable maintenance, they can preserve their impressively high-efficiency levels for years.

Cons of combi boilers

Unfortunately, combi boilers do have a disadvantage. They’re not suited for homes or properties with many users. If you have a large family with several bathrooms, a regular combi boiler might not work well.


Because of the several water outlets. The hot water will come out at low pressure if several showers are running simultaneously. If you’re not picky with your combi boiler, you might have to shower with small water trickles in the high traffic mornings and evenings.

So what’s the solution?

You’ll have to go with the specialized storage combi boilers. They can supply hot water to several outlets at the same time. Nonetheless, expect them to be pricier than your “average” combi boilers.


Are combi boilers worth it? Yes, they are more efficient, durable, and can help save on a lot of space. We hope this guide helped you as you consider changing from a conventional boiler to a combi boiler.

Do you need professional help? Call us today! We are ready and here for you.

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