Ultimate Guide to Worcester Bosch Oil-Fired Boilers

Why You May Need an Oil Fired Central Heating Boiler

Despite the use of gas-fired boilers in most UK homes, around 4 million homes are not connected to the main gas network. Thus roughly 1.5 million households heat their homes using oil.

Another reason for using oil for central heating is areas where the gas network was installed recently, and surrounding properties are not yet connected.

How does Oil Fired Central Heating Work?

Oil fired heating systems deliver heat in three ways – steam through radiators, warm air through vents, or hot water through baseboards.

A thermostat will sense the room temperature has fallen below its setting, before sending a signal to your heating system to generate heat for your home.

Once the oil boiler engages, heating oil will travel from the tank to the burner via a pump, where it turns into a mixture of fine mist and air. This mixture is then injected into the burner where the combustion chamber ignites.

Types of Heating Systems

Water-based and warm air systems work differently. Water-based systems have two main types – hot water systems and steam systems. Water heats up in a cast iron or steel boiler before its distributed throughout your home.

  • In hot water systems, heated water circulates through radiators or baseboards
  • In a steam system, water turns to steam before rising through the piping to the radiators.

In a warm air system, the furnace heats air, before a blower sends the heated air through the ducts and out the vents in your floor or walls. The air is then drawn back into the furnace through a return duct in a continuous cycle. Waste gas from the combustion will exit the system through a flue pipe.

Switching to Oil Heating

Oil heating systems make both economic and comfort sense. Before you decide to make a switch, a careful assessment of conversion costs is important.

Conversion Costs

Many people realise much later that the conversion cost of natural gas, electricity, propane or wood is much higher than initial estimates.

Here’s a checklist that can help you weigh the economics and comfort sense of switching:

  • Cost estimates of tank removal and disposal
  • The cost of comparable new heating systems and the fuel choice. Find out if there’re any special savings one can make
  • Compare efficiency ratings of the equipment and heat output
  • What are the installation costs?
  • Research fuel prices
  • Get the whole price inclusive of distribution charges, storage, delivery, and debt-reduction
  • Research other fuel providers – do they keep their promises, are your neighbours happy using their services?

For most households, efficiency measures such as upgrades and conservation techniques have the potential for great energy savings and higher returns on investment.

Cost of Installing Central Heating

Upgrading to central heating can save hundreds of pounds in heating bills per year. Apart from the complexity of laying the copper pipework for the heating system, this is a relatively straightforward task for an expert installer.

A two-story 4-bedroom home would take the engineering team about 5 days to complete the installation.

Zoning heating controls are important for energy efficiency. The controls separate different parts of your property into different heating zones. The system treats each floor as a separate heating zone, and only supplies heat to specific floors at set times.

How Much Does it Cost to Install an Oil Furnace?

Despite being a less common residential heat source, an oil-fired furnace is still a good investment for your home. It’s a good choice for increasing your HVAC system’s power and efficiency. Although oil furnaces are less efficient than gas and electric options, they cost 10% to 25% less and still provide enough heat.

Size and output of the furnace will depend on the size and age of your property. The average cost of installing an oil fired central heating in a four bedroom home can be up to £5,000.

You’ll also need to consider removal and disposal costs. Additional components such as a HEPA air cleaner can be added to a standard gas furnace – but they can be harder to coordinate with oil furnaces. Note the extra components will cost extra, though extra features can lower your monthly energy bills.

Buying and installing an oil furnace may be cheaper than other energy options, but maintaining it can be expensive.

Kerosene Boiler

Most oil-fired burners in the UK and Ireland run on kerosene by default. As a result, gas, oil, and diesel can fuel oil-fired home heating systems. Note that diesel or gas oil cannot fuel condensing boilers. Use them only on outdoor boilers that are fitted with a conventional vertical flue.

It’s important for a qualified boiler engineer to carry a kerosene boiler set up. Kerosene burners have a preheater installed to help lower the viscosity of the fuel and ease the workload on the pump. Since kerosene is a cheaper alternative, burning diesel/gas would make economic sense if you buy the fuel in bulk.

How long does a Boiler Last?

This question doesn’t have a straightforward answer. The millions of perfect boilers around the world from a technical view are likely to last 30 years or more. Despite the occasional breakdown, the main reason you would consider a boiler replacement is a breakdown needing parts that are no longer available.

Pros of Oil Central Heating

  • The high efficiency of oil will give you a good return on every energy unit
  • Modern condensing boilers which use hot flue gases are 90% more efficient than standard boilers


Cons of Oil Central Heating

  • The price of heat oil can fluctuate due to surges in demand, weather conditions and political unrest
  • Since oil delivery is by road, there’s a possibility of running out as you wait for the next shipment
  • Most condensing oil-fired boilers are floor standing. They need plumbing to allow acidic condensate fluid to drain out
  • Oil produces carbon dioxide which is harmful to the environment.



Oil-Fired Boiler Brand Guide

The Worcester Bosch brand is a market leader in UK’s domestic heating and hot water industry.

They are both convenient and practical options for homes that are not connected to the main gas supply.

With 30 oil-fired boilers in its current range to suit different home sizes there are many choices to choose from. This includes inside and outside installation sites.

Worcester Bosch oil-fired heat only boilers can operate alongside Worcester solar installations. You can choose to install oil-fired boilers under a kitchen worktop or fit it on the wall. The company has an extensive range of both internal and external oil boilers suitable for different types of properties.

Below we outline some popular Worcester Bosch oil fired boilers.

Greenstar Boiler Range

Worcester Bosch’s multi-award winning Greenstar boiler range has earned CORGI’s Boiler Of The Year award and Which? Best Buy award three years in a row.

Worcester’s Greenstar extensive range includes gas, LPG, and oil-fired boilers. All boilers in this range are A-rated efficient, condensing boiler types. The boilers are engineered to produce domestic heat, and hot water at lower energy costs – while reducing carbon emissions.

Greenstar boiler range includes wall mounted series, gas-fired boilers, and floor-standing models. Every boiler must undergo rigorous testing before leaving the factory.

The combi boiler design enables it to produce heat and hot water directly from the boiler. This is in contrast to regular and system boilers which heats your central heating system directly and produce hot water for your cylinder.

Greenstar gas, oil, and LPG boilers all function at 90% efficiency. They rank class 5 – the lowest of 5 categories – for nitrogen oxide emissions.

Worcester Bosch also takes advantage of renewable energy to produce ground source heat pumps, and air source heat pumps.

Greenstar Heatslave II

The Greenstar Heatslave II series is UK’s most popular external oil-fired combi boiler. This boiler type provides heat and hot water directly from the boiler instead of a water storage tank. The boiler is available in 12-18, 18-25 and 25-35kW outputs.

The boiler comes in various models which are suitable for any property size.

It features a strong IP45 weatherproof cabinet that offers protection from adverse weather.

The one-piece stainless steel primary baffle and innovative cross-firing burner allow for quick installation, servicing, and maintenance.

As long as there’s access for servicing, this floor-standing boiler which measures 85.5-by-52-by-60cm can fit under a kitchen worktop.

Extra benefits such as a pre-heated thermal store provide instant hot water and an optional 7-day plug-in timer for added luxury.

The boiler is a space saver adding the convenience from mains pressure water flow to your shower and taps.

With a SEDBUK 2009 efficiency rating of 89.4%, the Greenstar Heatslave II is quite to operate making it ideal for internal installation.

Greenstar Heatslave II External

This external boiler type has same features as the internal model. The design allows you to fit it outside, and is suitable for any home size with one or two bathrooms. The boiler’s strong cabinet offers protection for all weather.

A stainless steel primary baffle allows for quick servicing and maintenance. The layout is enhanced by a cross-firing burner for easier installation and servicing.

The latest range of oil-fired combi boiler series features the innovative Heatronic 4i control unit. This enables accurate and smart control of the boiler. This boiler range is perfect for homes with less space, and with no access to a mains gas supply, especially in rural areas.

To get the best quote for an efficient boiler, it’s advisable to shop around established boiler installers such as Hassle Free Boilers. Buying from an established company could save you hundreds of pounds in future repairs and service. Have a Gas Safe engineer do the installation to ensure your property’s safety.


Worcester Oil Combi Boilers

Most Oil combi boilers are larger than gas or LPG boilers with a majority being floor standing. Worcester Bosch is the pioneer of the combi boiler in the UK, with the Greenstar range the most popular of the lot.

Worcester Bosch combi boiler is a combination of a high-efficiency water (A-rated) heater, and a central heating boiler in one single unit. They’re cheaper to run and energy efficient as the water heats up instantly instead of pre-heating, then storing in a cylinder.

Greenstar combi boilers are engineered to perform and operate efficiently. They have a ‘keep hot’ device that ensures hot water is instant whenever it’s needed.

This boiler type integrates a unique ‘ECO’ mode button which overrides the ‘keep hot’ ability. In the process, less gas is used as energy is only utilized when you need hot water.


  • It’s compact size makes it ideal for small homes
  • Suitable for properties with little or no loft
  • The lack of a hot water cylinder increases living space
  • Reduced risk of loft pipework freezing
  • Less pipework involved makes installation cheaper

Worcester External Oil Combi Boiler

An external oil-fired combi boiler is perfect for a home that is too small for an indoor oil fired boiler. It’s the best boiler type if it’s not workable to have an internal boiler.

The encased, insulated, and weather-proof cabinet allows for external fitting. In case of extreme cold, a built-in frost thermostat adds protection throughout winter.

You can install a Worcester External Oil combi boiler on the floor or on the wall.


  • They save on space and can fit well in the kitchen
  • Ideal for smaller properties

Worcester Oil Fired External Combi Oil Boiler

Apart from using oil for fuel rather than gas, this boiler type is same as the gas fired boiler. As they’re not connected to a gas network, it means ordering a tank of oil from a supplier. You’ll need a storage tank for refilling, with a connection to the boiler which automatically feeds it fuel.


  • More space indoors
  • Less noise as some boilers are noisy when running
  • No risk of carbon monoxide occurrence
  • Prevents damage to property in case of oil leaks
  • An external boiler is easier to access for servicing
  • More heating for outdoor buildings

Worcester Approved Oil Boiler Installation

You can only buy Worcester boilers through suppliers such as Hassle Free Boilers. This is because Worcester doesn’t sell directly to customers.

In case you have a boiler breakdown during the manufacturer’s guarantee period, contact your installer first to ensure it’s an appliance fault. During this period, Worcester Bosch parent company will cover the repair costs of components that are faulty or defective. But you must register within 30 days to qualify for the guarantee which can be extended by between 3 and 7 years.

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