Combi boiler prices remind me a little of airline tickets. When you start the process of searching, the price initially looks great – but by the time you’re finished adding the extras, your credit card isn’t looking too healthy.

In this guide we want to help you understand what a combination boiler is, what you’ll pay to have a new one installed, and how much it might save you in the long run. That way you can make a good decision when and if you need to get a new boiler.

What is a combination boiler?

When a UK homeowner decides to get a new boiler, there’s a pretty high chance they’ll opt for a wall-mounted gas combination boiler – or what most of us call a ‘combi boiler’. These small gas-fired boilers make up about 74% of the market for new boilers purchased in the UK.

So what is a combi boiler? A combi boiler is a system that provides both heating and hot water directly from one boiler, hence the name ‘combination boiler’. In the UK when we talk about a ‘combi boiler’, we’re generally talking about one using natural gas. Electric and oil boilers do exist, but should be avoided where possible due to high fuel costs.

Since 2005, pretty much all new gas combi boilers have been wall-mounted condensing units. This just means that they’re small and efficient models, mounted on the wall and thus without the need for external tanks. The fact that combi boilers are compact, economical, use mains pressure and are quickly installed has led to them becoming the preferred boiler choice in the UK.

Despite these advantages however, there are some situations in which a gas combi boiler is not necessarily the best choice. Let’s take a look at a few:

1. Off the gas grid: Without gas the typical boiler options are electric storage heaters and oil boilers.
2. Simultaneous hot water: If you often need to run multiple hot taps at once, a combi boiler won’t be ideal. For some bigger households in this situation, a system boiler or conventional boiler with a tank is a better choice.
3. Low water pressure: Combi boilers rely on mains water pressure to move hot water about the house. If your water pressure is poor, then a system or regular boiler may be a better option.

If, however, you live in a small- to moderate-sized household on the gas grid, with decent water pressure to boot, then a combi boiler could be an ideal replacement boiler.

Now, to pricing: it’ll help to understand what a new one might set you back.

Combi boiler prices, installation costs and extras

One of the common mistakes people make when considering a new boiler is to simply google ‘combi boiler prices’ – the search results would have you think a new boiler can be installed for less than £1,000.

Sadly, this just isn’t the case. Depending on the size of the combi boiler required, the difficulty of the labour involved and the need for any extras, you can expect to pay £1,500 – £4,000 in most circumstances – with an average, fully installed boiler costing about £2,300 (according to the Energy Saving Trust).

1. Choose what size boiler you’ll need
2. Add an estimate of the installation costs
3. Be prepared for the possible extras

Let’s say you’ve got a relatively modern flat with an existing gas combi boiler that needs replacing. This might cost £700 for the boiler, £600 for the installation, and another £150 for a magnetic filter, bringing the total to £1,450 – about as cheap an install as you’re likely to get. Add a ‘power flush’ if there happened to be sludge in the system, and you’re quickly up to £1,950 – still, not bad.

At the other end of the spectrum, however, let’s say you have a large home and are switching to a combi boiler in a new position. The boiler will cost £1,500, and the install £1,100. A power flush with lots of radiators might be £700, extra pipework £300, a new thermostat £200, and a magnetic filter £150. Suddenly, it’s £3,950.

These two examples are, of course, just estimates – but they give you an idea of why prices can vary so much. The sensible way to make sure you don’t get stung is to get multiple quotes, and ensure that what you are being offered is itemised in the bill. As long as all your quotes are itemised, you’ll be able to tell if you are paying more for the boiler, labour or other equipment – and be in a good place to understand what you are getting for your money.

How much can replacing an old boiler save me?

A prevalent question – and thanks to the good people over at the Energy Saving Trust, one we can answer with a decent estimate, based on your house size and existing boiler efficiency. In the chart below, I’ve taken the numbers and crunched them.

This graph estimates the annual gas savings that could be made when switching to a more efficient boiler. As you might expect, the less efficient the old boiler is (G is the lowest rating) and the larger the house is (detached homes need the most heating), the more savings that can be made.

For example, changing from an E-rated boiler to a new A-rated combi in a mid-floor flat only saves £90 a year on gas; replacing an F-rated boiler in a detached house, however, could save £430.

Let’s put these figures into context. If you replaced a highly inefficient G-rated boiler in a semi-detached house, the expense might pay itself back in gas savings after seven years. Replacing a D-rated boiler in a flat, however, could easily take 20 years to pay off. The efficiency gap between old and new is the main factor driving the difference.

Which leads us nicely to our last question.

Is it time for a new boiler?

A good question – but one that only you can really answer. Weighing the costs and benefits can help you think it through. Let’s take a look:

The benefits:

1. Savings: If your old boiler is quite inefficient there’s a good chance you can cut your gas bill by 20-30%, as we’ve just detailed
2. Reliability: A well-installed combi boiler is very reliable, and often comes with a five-year warranty when fitted by an accredited technician
3. Availability: Moving to a combi boiler ensures you enjoy a permanent hot water supply, and don’t have to wait for filling tanks
4. Space: Switching to a combi boiler can reclaim space used for water tanks
5. Pressure: Mains pressure showers are rather nice really
6. Maintenance: Much like a new car it shouldn’t bother you for at least five years
7. Safety: A well-installed new boiler can improve safety, along with having the appropriate carbon monoxide detector fitted with it

The costs:

1. Cost: Expect to pay £1,500 – £4,000 in most circumstances
2. Time: It will cost you a little time to organise a new one
3. Hassle: Finding a good registered installer is crucial to your success
4. Choice: You will need to research which boiler to buy

Lastly, here are a few examples of when you should really consider upgrading to a new boiler. If you are in one of these five positions, give it some serious thought.

1. High cost repair: If something goes wrong in an old boiler that requires more than £500 pounds to fix, you may be better investing in a new boiler and being rewarded with lower bills
2. Recurrent breakdowns: Not having heating or hot water during winter is both inconvenient and stressful. If an old boiler is requiring a lot of small repairs and causing you anxiety, consider replacing it
3. Flue problems: The flue is essential for both safety and function. Repairing one is invariably expensive and is money better spent on a new boiler
4. Moving your boiler: If you are moving an old boiler as part of renovations being made, consider upgrading. You will already be paying for much of the required labour, so the additional cost of the boiler is worth it
5. Old boilers: Although many older boilers can last for up to 30 years, they are likely to be highly inefficient. In such cases the cost of capital for a new boiler is significantly below the annual savings. In other words, it makes sense purely as a financial investment

The last example is the most relevant to people who aren’t swayed by a boiler breakdown. When you consider the average gas bill for a large house is almost £1,000, and that replacing it may save around £250 a year in gas costs, then the £2,500 it might cost for a new boiler would have a crude payback of around ten years. If you were intending to stay in that house and could reap both performance and reliability benefits, it would certainly be a good investment.

If you do opt for a new boiler, make sure you get three properly itemised quotes. Choose a boiler from an established brand that includes a guarantee, and ensure the work is done by a gas safe registered engineer.

If you do go down the route of getting a new boiler make sure you get three properly itemised quotes. Choose a boiler from an established brand that includes a guarantee and ensure the work is done by a gas safe registered engineer.

You can also look into getting a new boiler on finance.

And finally, don’t forget to consider what you are paying for gas in the first place.