Changing From a Conventional Boiler to a Combi Boiler [Cost Guide]

Looking to change a conventional boiler to a combi, but not sure if it’s the right move?

No problem! This guide will cover everything you need to know before making the switch, and even show you how to get an immediate, no-obligation, fixed quote for your combi conversion

Changing from conventional boiler to combi

Is Changing From a Conventional to a Combi Boiler Worth It?

Yes — in most cases, changing to a combi boiler is a worthy investment. That’s because combi boilers take up less space, heat water on demand, require less maintenance, and are generally more efficient.

However, there are circumstances in which your replacement boiler should be a newer conventional boiler model rather than a combi. For example, if your household uses lots of hot water at once — which is true of many larger families — a combi boiler may not keep up with the demand. This means that during peak usage times, like morning and evening, the water pressure in your taps may be greatly reduced to a trickle.

If you want to see what your optimal replacement options are — whether conventional or combi — we suggest you use Heatable’s calculator. You’ll have to answer a few quick questions about your existing boiler and property, and you’ll get fixed quotes for a range of boiler options on your screen immediately. I recommend that you do this calculation twice — this will get you separate quotes for combi and conventional boilers, which you’ll then be able to compare.

How Much Will Changing From a Conventional Boiler to a Combi Cost? 

Typically, you’d be able to get a combi boiler installation for a small-medium property for roughly £1,800-2,000. However, changing from a conventional boiler to a combi is a lot more work than simply switching a broken appliance, with a new one. Here are a few extra costs you can anticipate in a combi conversion:

Cost to Remove Hot Water Tank and Cold Water Feeder Tank

If you’re changing from a conventional boiler to a combi, one of the biggest benefits you get is all the extra space freed up as you remove the water storage tanks. Of course, their removal isn’t free; typically, you can expect to pay between £100-£150 for this procedure alone.

And that’s not all — regular boilers also come with a cold water feeder tank, which be should be removed as well. This typically costs between £200 and £300.

There are a lot of other factors that will affect the installation price. But overall, assuming your combi conversion is a simple one, you should expect to pay around £2,700-£3,000. 

You can use a cost calculator and get a fixed price on-screen for your combi conversion, which will account for all of these factors.

Heatable boiler clickable form

What’s Involved in Changing to a Combi Boiler

Combi conversions vary when it comes to the workload. And naturally, the increased workload means an increase in price. Here are a few essential steps that typically comprise a combi conversion:

  • Moving a boiler to a new location
  • A new core hole needs to be drilled for a flue in a new location
  • The gas run needs to be upgraded to current standards
  • Heating controls need to be upgraded from the originals
  • The installation of a magnetic system filter (advised), and a limescale filter (advised for hard water areas)
  • The installation of TRVs
  • Type of boiler warranty (i.e. a low budget appliance with a 2-year warranty, over a leading brand with 5-10 years warranty).

Other things that increase the price of changing from a conventional boiler to a combi, rather than a straight combi swap, include:

  • Removing the old hot water cylinder
  • Removing the cold water feed tank (usually in the loft)

As you can see, it’s not a one size fits all approach.

Reasons For Changing to a Combi

The average household is suited to a combi boiler. Unless you have a high demand for hot water and heating (dozens of radiators, and several showers running at once), there’s a good chance a combi boiler is for you.

Even if your family has a high demand for hot water and heating, there might be a storage combi boiler to suit.

To double-check, you can use this boiler size calculator, which will offer up the best solutions based on clickable multiple-choice questions it asks about your property.

So, what are the benefits of upgrading to a combi boiler, over your existing conventional setup?


Unlike a conventional boiler, a combi heats hot water on demand, rather than having a constant supply of water being heated in a cylinder; that makes them more efficient.

The Energy Saving Trust estimates extremely old boilers in large properties, could be costing an additional £305 per year compared with a new one, and that doesn’t even factor in efficiency savings from your combi upgrade.

Space Saving

If you’ve ever been house hunting, the likelihood is, you’ve come across more than one redundant airing cupboard in your time. Most likely, the pipework has been capped, the cylinder that it used to house has been removed, and the property’s heating system has been upgraded to a combi.

You’ll save tonnes of space when changing to a combi. Not only can you remove the cylinder from your airing cupboard and the cold feed tank from the loft, but there are also plenty of manufacturers offering compact boilers, which will sit in a standard sized kitchen cupboard.

For larger properties, that bonus might mean freeing up kitchen space and improving aesthetics, by removing a wall hung boiler. For flats and apartments, where space is prime, it’s extra storage that you wouldn’t have had otherwise.

What kind of fuel does your boiler use?

Grab your fixed price online by 3PM, and get next-day boiler installation.

Worcester boilers installed from as little as £1,795.

The Best Combi Boilers to Install

There are tonnes of incredible models and reputable manufacturers from which to choose.

Typically, you can use the criteria below to narrow down your options:

  • kW output – is the boiler powerful enough for your property?
  • Physical dimensions – will you need to fit it into a small space, such as a kitchen cupboard?
  • Warranty – does the included warranty show the manufacturer’s confidence in their product?

Regarding the latter — we’d not suggest sacrificing warranty to save £100 or so on a new boiler. Why? The installation could be costing you upwards of £2,700, but the boiler is only to make up around 40% of that cost.

If you want to go with products from brands that have confidence in their OWN products’ longevity, we’d suggest choosing one that has a warranty to match. Typically, that means going for a 5-year warranty as a minimum. However, there are boilers with 10 year warranties, so if your budget can handle it, it’s going to be money well spent.

If you want to see which boilers will suit your property best, you can fill in this quick, anonymous form from Heatable and get the model options — along with fixed installation quotes — on your screen in minutes.

Which Installer Should You Choose For Your Combi Conversion?

There are literally thousands of installers across the UK. Some are small and local, some are national. And from what’s available, you’ll see a huge differential in prices quoted for the same job.

Our suggestion? Get researching, and get some prices.

For smaller local installers, you can jump over to this network, and request up to 3 quotes from installers that work specifically in your area.

National companies tend to be much more expensive. However, we find Heatable is always worth a look.

Heatable new boilers

They use an automated online quote system, removing costs associated with other national firms (phone reps, on-site salespeople, and so on) and that means they tend to be on par with local installers in terms of prices, rather than national installation companies.

You can check the prices for them here.

What’s Next?

Hopefully, that’s everything you need to know before changing from a conventional boiler to a combi.

Got questions? Drop us a line through our contact form, and we’ll get back to you ASAP.

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