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Oil Boiler Cost: 2023 Replacement Combi Price Comparison UK

Everyone needs hot water and heating to make life comfortable. But, which boiler do we choose, and what is the cost of a new boiler?   

Most people agree that gas is the cheapest, cleanest fuel. But, if you live in a rural part of the UK without mains gas, the next best thing is an oil heating system. 

On average, oil fired central heating boilers plus installation, cost between £2500 and £4500. The required heating output varies depending on many factors that we’ll go into later. But, the most popular oilfired boilers output from 18kW to 44kW. 

So, how does an oil boiler installation differ from gas, and what are its benefits? 

The most obvious difference is the fuel. Oil fired boilers burn heating oil (kerosene) to provide heat, while mains gas boilers use Natural Gas.  

The next difference is that you can use heating oil anywhere in the UK. As long as you have room on your property to keep an outdoor oil storage tank, you can receive delivery by lorry and store it in a tank on your property. In contrast, Natural Gas requires permanent gas plumbing from the supply, while electric heating depends on a National Grid connection. 

Gas is the cheapest traditional heating fuel. But, you probably don’t have mains gas to your property if youre reading this. So, let’s ignore gas and concentrate on the other fuels. In April 2020, the Energy Saving Trust said the average oil price in England, Scotland and Wales was 4.81p/kWh. In comparison, the price in Northern Ireland hovered around 4.69p/kWh. 

Compare this to wood pellets (5.99p/kWh) and electricity (16.36p/kWh). Remember that we aren’t comparing renewables here such as heat pumps, solar and wind devices. These, after the initial capital outlay, and a small electricity supply, are effectively free to run. But, not everyone has space or opportunity to use renewables. 

Therefore, out of the existing ‘traditional’ heating methods, oil is the most convenient and least expensive. Likewise, a combi boiler is probably the most efficient way to heat water and run a central heating system for most people. Look at this section to determine the difference between the various boiler types and how they’re used 

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How Much Do New Oil Boilers Cost? 

Generally, oil boilers cost more to buy than gas. But, if you don’t have gas available, you haven’t got much choice. In the table below, you’ll find an oil boiler cost calculator. You can use this to calculate installation prices and the approximate cost of a new oilfired combi boiler, by comparing it to your situation. Remember that other oil-fired combi boilers are available. But, the oil boiler prices shown below come from a few different online resources and represent an average. The actual prices depend on: 

  • The size and heat output needed for your oil boiler installation 
  • The manufacturer and the heating engineer who installs the boiler. On average, the cost to install an oil combi boiler ranges from £500 to £1000.
Boiler typePower output (kW)Price
Warmflow Utility Combi 21, 26, 33£1300 to £2000 
Grant Vortex Blue Internal 21, 26, 36 £1500 to £2500 
Mistral Combi Standard 20, 26, 35 £1900 to £2200 
Firebird Envirogreen Combi  20, 26, 35 £2000 to £3000 
Worcester Bosch Greenstar Heatslave II  18, 25, 32 £2300 to £2400 

If you haven’t enough room indoors for your boiler, most manufacturers offer external oil boilers for permanent outdoor installation. These need a weathertight covering, usually a  sealed box with doors for maintenance. Speak with a professional OFTEC heating engineer for advice on the boiler type suitable for your property.  

Types of Oil Boilers 

The deciding factor to determine which type of oil-fuelled boiler you need, comes down to how much hot water you want. This amount equates to the number of hot water outlets you expect to use simultaneously and the number of radiators in your house. So, the power output, and the type of boiler determines which one you should use for a specific job. If the boiler is too small, then you won’t have enough hot water. If it’s too large, it uses more fuel than you need, which increases the running costs. Finally, whichever boiler you choose, install an oil storage tank outside to hold the fuel. 

Combi boilers 

Combi boilers are great for a small house. They don’t need a cold water tank or a hot water cylinder. Because, they only heat water on demand directly from the domestic cold water mains, so won’t lose heat from stored hot water. They are perfectly suitable for supplying the hot water and heating requirements for homes with 1 or 2 bathrooms. 

Combi boiler prices range from around £1000 to about £4500 depending on the make and model. 

System boilers 

System boilers provide hot water like a combi, by heating cold water directly from the mains, rather than from a cold water tank in the loft. However, they also need a hot water cylinder to store hot water for multiple bathrooms, sinks or washbasins. Generally, a system boiler with a heat output of 28kW to 34kW can provide enough heat for up to 20 radiators.  

Typical prices to purchase a system boiler range from £1000 to £3000, plus installation. However, suppose you install a system boiler from scratch. In that case, it comes as part of a heating system, so you’ll also need a hot water cylinder and lots of plumbing too.  

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Conventional boilers 

Conventional boilers, also known as ‘regular’ or ‘heat-only’ boilers, provide heat for a traditional heating system.  These boilers don’t heat water directly from the mains. Instead, they receive water from a cold water storage tank situated in the loft. These boilers need a cold water feed tank, an expansion vessel, and a hot water cylinder to operate successfully. They heat the central heating system directly from the boiler but store hot water in the cylinder. Typically, conventional boilers cost between £1000 and £3000, plus you’ll have to include any costs associated with the remainder of the system such as plumbing, tanks and a cylinder if they need replacing too. 

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Oil Boiler Models 

Let’s look at a few of the models available to see what features they have and how they fit the overall scheme. We consider all three boiler types and specifically one from each end of the power output spectrum. Generally, oil boiler companies try to produce a model to suit just about any circumstance. So, don’t worry if you can’t find one here that suits you. There are plenty more models available, which is a bit daunting for the amateur to wade through hundreds of oil-fired boilers. All you have to do is speak to a qualified and registered OFTEC heating engineer. By the way, all prices include VAT. 

Combi boilers 

The Firebird Enviroblue HEC20 Combi Internal 2kW Oil Boiler is a floor standing, oil-fired condensing boiler. It produces 16L/m of hot water with a maximum central heating output of 20kW (Other outputs range from 20kW to 35kW). Its ERP Rating is very good with heat production rated at ‘A’ while the hot water rates at ‘B’. The boiler has a standard warranty of 2 years and an overall efficiency rating of 93%. 

Typically, the average cost to buy this boiler would be about £2400. In comparison, installation fees would be between £500 and £1000. Therefore, you can expect a total cost of between £2900 and £3400. 

At the other end of the ‘combi’ spectrum, The Worcester Bosch Greenstar Heatslave II 25/32 Combi Oil Boiler is also a floor standing, oilfired condensing boiler. It produces a flowrate of 22L/m hot water with a central heating or hot water maximum output of 32kW. However, boilers producing 18kW and 25kW are also available. Its ERP Rating is very good with heat production rated at ‘A’. And, hot water rated at ‘B’. The boiler has a standard warranty of up to 5 years and an overall efficiency rating of 91%. 

Installation fees fall between £500 and £1000, with an average purchase price of around £2300. In total, the full cost to install this boiler would be between £2800 and £3300. 

System boilers 

At the lower end, the Worcester Bosch Greenstar Danesmoor 12/18 System Oil Boiler is a floor standing, oil-fired condensing boiler. It has an ERP Rating of ‘A’ for heat and provides a central heating maximum output of 18kW. However, other versions in this range supply 25kW and 32kW. And, there is an ‘External’ version specifically for outdoors installation. 

Typical oil boiler replacement costs fall between £500 and £1000 for installation. Moreover,  the average price to buy this boiler would be around £1750. So, the total installation cost for this boiler would lie between £2250 and £2750.  But, if you also intend replacing the hot water cylinder, you increase the costs accordingly. 

At the upper end of available system boilers, we have the Mistral Sealed System S3 35kW Oil Boiler. This boiler is also floor-standing but is a non-condensing boiler. It has a ‘B’ ERP Rating but has an overall efficiency of 87%.  

The boiler produces a maximum heat output of 35kW. But other models in this range produce up to 20kW, 26kW, and 41kW. Finally, the model has a warranty for 2 years covering general parts, and 5 years covering the heat exchanger. 

For this oil boiler, cost to replace totals £2000 to £2500. This figure comprises an average purchase price of £1500 and installation costs of between £500 and £1000. 

Like all system boilers, this model sends hot water to the central heating system and a hot water cylinder. So, if you intend replacing this additional hardware, you must add on the appropriate amounts to the total price. 

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Conventional boilers 

At the low end of the scale, the Grant Vortex Pro External 21kW Regular Oil Boiler is a floor standing boiler like the others. But, this one is specially designed to fit outside your property. The boiler has a radio frequency (RF) transmitter to allow wireless remote control anywhere in the house. This boiler has an ERP rating for central heating of ‘A’, and a ‘B’ rating for hot water. It is also 90.7% efficient, more than other external boilers in the Vortex External Eco range. This version produces a heat output of up to 21kW. But, if you need more, because you have a large house with more radiators, the manufacturers also produce a 26kW, 36kW and a 46kW version. A standard 2year warranty covers all parts, plus it has a 5year guarantee for the heat exchanger. 

This models typical purchase price is around £1250, with installation costs of £500 to £1000. Therefore, total cost sits between £1750 to £2250. 

Looking at the high output end of the scale, we offer the Warmflow Kabin-Pak K150HE 44kW Regular Oil Boiler. It has an ERP Rating of ‘A’ for heat and is 90.3% efficient. This condensing boiler produces a heat output of up to 44kW. But, also has 21kW, 26kW, and 33kW if you need less 

The boiler’s typical purchase price hovers around £1900, with installation costs of between £500 to £1000. Therefore, the total cost lies between £2400 to £2900. 

Oil Boiler Running Costs 

Gas is the cheapest fossil fuel at present in the UK. But heating oil (kerosene) is a second-best when used in an oil-fired boiler to fuel a central heating and domestic hot water system. However, the price of kerosene can fluctuate. According to the Energy Saving Trust, kerosene prices in April 2020 were typically 4.81p/kWh compared to 4.17p for gas, 7.19p for LPG, 5.99p for wood pellet. Furthermore, standard rate electricity was 16.36p, and the Economy 7 tariff was 9.76p/20.03p. Additionally, both electricity and gas have standing charges of around £90/year, associated with their running costs, whereas oil doesn’t. So, you can see that heating oil is much cheaper than other fuel types (excluding gas). 

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The costs outlined in this article so far deal only with the purchase and fitting costs of various boiler types. But, there are more costs associated with these, which we’ll look at now. 

Balanced flue 

Every boiler needs a flue for ridding itself of waste gases. They also need fresh air for combustion. The ideal method here is a balanced flue. The boiler usually fixes to an external wall so the flue can go through the brickwork immediately. Sometimes the flue runs vertically up the house’s wall. In which case, each length of balanced flue pipe costs around £90. 

Plume Management Kit  

The last thing you want to happen with the boiler’s toxic waste gases is for them to enter open windows. So, this kit costs around £150, plus £60 for each 1m additional extension. 

Flexible Liner Kit 

Many installers use existing brick chimney flues as a way to divert waste gases to the open air. However, chimneys need linings to prevent the gases from seeping through mortar joints into the house, and to provide an appropriate draught for the gases. The best and easiest way to retrofit a brick chimney, so its suitable for oil boiler waste gases, is to use a flexible flue liner kit. These cost around £400 and must be cut to length. 

Fire Valve 

If the boiler temperature rises above 85°C, then the house is probably on fire. It’s a good idea to turn off the oil supply to the boiler, in situations like this. The valve sits outside the house on the pipe just before it enters the house, with new installations. Prices for this range from £80 to £120. 

Oil Filter 

Many debris types end up in the oil tank, especially if you have an old tank, starting to corrode. If this stuff ends up in the boiler, it blocks the spray jets in the combustion chamber. So, you need a filter to collect the debris. Prices start at around £80. 

Oil tank 

You need somewhere to store the heating oil, so it’s safe, secure, and prevents as much debris as possible from entering the oil. If you have an old oil tank already installed, and the OFTEC heating engineer advises a replacement. Don’t delay getting one. Take the engineer’s advice on size and type too; after all, they are the experts. 

Costs to buy an integrally bunded oil tank ranges from £1100 to £2000 depending on size. Typically, a 1200 litre slimline tank costs around £1500. 

You also have to install the tank too. A small tank costs around £2000 to install while a large one costs around £3000, including installation of tank and base. Additionally, you need a new oil line (around £500) and transferring the oil from the old tank to the new one (£300). 

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The heat output of the boiler must match the number of radiators you have in your home. Certainly, not a job for the amateur. Leave this to the professional who probably already has a spreadsheet set up to calculate the amount of heat needed. They also consider the amount of insulation you have, the property type, and other relevant factors. The amounts calculated below aren’t accurate, as we shouldn’t just take the number of radiators into account. You also have the three types of boiler to consider (combi, system & conventional). The combi is the most efficient until you reach a certain number of radiators and bathrooms. Then you have to choose whether to use a system or conventional boiler. These don’t always need such a large power output, as the hot water gets stored in a cylinder. So, it’s only the central heating that counts. 

To calculate the running costs, lets assume the following: 

  • Oil price of 4.81p/kWh. 
  • The boiler runs at its maximum power output. 
  • Boiler runs for 6 hours per day for 6 months of the year to heat the radiators. 
Type of property Radiators Power (kWh) per day Average cost per annum 
Small house or flat 10 radiators & 1 bathroom 24kW x 6hr = 144kWh4.81p/kWh x 144 x 365/2 = £1261
3 bedroom house 15 radiators & 2 bathrooms 30kW x 6hr = 180kWh4.81p/kWh x 180 x 365/2 = £1580
4 bedroom house 16 radiators & 1 bathroom 35kW x 6hr = 210kWh4.81p/kWh x 210 x 365/2 = £1843
4 bedroom house 18 radiators & 2 bathrooms 37kW x 6hr = 222kWh4.81p/kWh x 222 x 365/2 = £1948
5 bedroom house 20 radiators & 3 bathrooms 40kW x 6hr = 240kWh4.81p/kWh x 240 x 365/2 = £2106

Oil Boiler Benefits 

An oil hot water boiler isn’t suitable for every home in the UK. But, they have many benefits that might convince you to choose one of these boilers above many others. 


Oil combi boilers are extremely energy efficient as they heat domestic water on demand. Therefore, you don’t store hot water in cylinders and don’t lose heat, thereby reducing the amount of energy used. Thus, making big savings on the fuel bill. 

Running costs 

An oilfired boiler’s running costs are very much lower than many other fuel types (except gas). However, oil is a more efficient fuel for modern boilers than gas, you get more heat from each unit of oil, so you get a better return. 


Many rural regions of the UK don’t have mains Natural Gas. Therefore, the only feasible alternative is to use heating oil. 


You don’t have a constant supply such as electricity or gas, and you pay for an oil delivery when you need it. Therefore, you don’t have awkward supply contracts, and you can change supplier at any time. 

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Compatibility with renewables 

Many oilfired boiler owners use it as a back-up alongside renewable energy sources such as wind and solar. 

New boilers compared to old 

New oilfuelled boilers have an efficiency of between 92% and 95%. Compare this with older systems that were only 60% to 70% efficient. 

Oil Boiler Disadvantages 

Believe it or not, there are disadvantages to using oil fired water heating as well as benefits. 

Fuel costs 

At present, oil is the second cheapest fuel for use in domestic heating boilers. But as time goes on, expect oil prices and other fossil fuels to increase as they become scarce. 


Oil is only delivered as you need it and as your tank starts to run out. Unlike gas or electricity, you might run out before you can get your next delivery. 


All heating boilers need servicing. But, some need less maintenance than others. Oil fired boilers need regular servicing and need oil tank maintenance as well. 


Although uncommon, if your oil tank is within easy access of the road, you might find your oil level dropping overnight. Always secure your tank with a sturdy lock, and fit an alarm that triggers if the oil level drops rapidly. These alarms are also useful if the tank accidentally springs a leak. 

Heating Engineer Hiring Checklist

  • All oilfuelled boilers and heating oil tanks can only be serviced and maintained by OFTEC registered heating engineers. Ensure the registered heating engineer has an ID card that hasn’t expired. 
  • Use the Rated People website to check other people’s experiences. Also, ask locally for recommended oil heating engineers. 
  • Ask for a quotation for the work. The quote should contain a detailed description of the job, a price, and a payment schedule. 
  • Find out if the tradesman is VAT registered. If he is, ask for the quotation to include VAT, as many professionals don’t automatically do this. 
  • Find out if the engineer offers any guarantees for their work. Make sure you know how long the guarantee is in force. And, that you have the relevant paperwork. 

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Oil Boiler FAQ 

What is the life expectancy of an oil boiler? 

This depends on the quality of the product and the reliability of the manufacturer. However, you can expect a typical boiler to last from 10 to 15 years. 

How long does it take to replace an oil boiler? 

The time depends on whether you are replacing like-for-like or changing to a different type of boiler. For example, if changing from a conventional to a combi. 

To swap a combi for a combi, you can expect the job to take 4 to 6 hours. 

To remove a system or conventional boiler and replace with a combi, you should expect about 2 days. 

If you have a back boiler and swap it for a combi, expect it to take from 2 to 3 days. 

If you want to move your boiler to a different place within your property, expect at least an extra 4 hours depending on how much more pipe run it needs. 

How efficient is an oil boiler? 

A typical new condensing oil fired boiler is between 92% and 93% efficient. On the other hand, a non-condensing boiler is around 85% efficient. In comparison, an old heating system would usually be between 60% and 70% efficient. 

Are oil boilers being phased out? 

All fossil fuels are phasing out, to be replaced with more sustainable heating methods instead. However, this doesn’t mean the end of oilfuelled boilers. We expect low carbon biofuels to take the place of kerosene within a few years. 

What can I replace my oil boiler with? 

There are plenty of alternatives to oilfuelled boilers. Some might be more costeffective, while others might be less. Some fuels that might cost much more than you can afford might reduce in price with increased demand or better technology. Also, some methods might not be at all feasible for your situation.  

The alternative fuels available are: 

  • Natural gas (also called North Sea Gas) is the cheapest fuel, but not everyone has access to it. This situation might change in the future. 
  • Heat pumps draw energy from the ground or the air. They only use as much electricity as a small fridge, so they are very economical. 
  • Wood pellet boilers are more expensive to purchase than oil or gas boilers. You also need a large bulk storage room that’s free from damp. 
  • Electric heating is expensive to purchase the boiler and to produce heat. The only advantage is that regular maintenance is much cheaper, and very few parts wear out. 

Is heating a house with oil expensive? 

Heating a house with oil is a bit more expensive than using gas, but much cheaper than other ‘traditional’ heating methods.  

Fuel prices in April 2020 were as follows: 

  • Natural gas – 4.17p/kWh. 
  • Heating oil (kerosene) – 4.81p/kWh. 
  • LPG (bottled gas) – 7.19p/kWh. 
  • Wood pellet – 5.99p/kWh. 
  • Standard rate electricity – 16.36p/kWh. 

Oil Boiler Review

Installing a modern oil fuelled boiler might be a better choice if: 

  • You aren’t on mains Natural Gas. 
  • You currently use one of the other fuels. 
  • Your old boiler isn’t efficient. 

If you are on this list and don’t know what an oil boiler costs, its probably worthwhile asking an OFTEC registered heating engineer to give a quote for installing an oil fired boiler. 

Complete the form on this page, and you’ll receive 3 or 4 quotes from registered heating engineers near you.

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