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Witten by Bernard Morgan (Engineer) & Adam Apperley (Marketing). Published: January 24, 2018. Updated: February 19, 2024

Grant vs Worcester Bosch

When it comes to a Grant or Worcester oil boiler which is the best?

Grant and Worcester Bosch offer some of the best oil boilers money can buy in the UK. At Boilerhut, we’ve taken a look at both brands. Comparing their best-selling oil boiler models and looking at the pros and cons in detail.

About 4 million households are not connected to the UK’s gas network. For these homes living off the mains gas grid, oil and LPG are the two best fuels to power a central heating system.

However, oil is a more energy-efficient and cost-effective fuel compared to LPG. There are a few options for oil boilers out there. Grant boilers and Worcester Bosch are the two best and biggest manufacturers of oil boilers in the UK.  Let’s take a closer look at each brand.


Grant UK Engineering has been designing and manufacturing heating products for over 40 years. Their range of oil-fired boilers is highly reviewed. They are often favoured above other brands by reputed review magazines and websites.

Grant’s oil-fired condensing boilers range has a reputation for quality and reliability, on top of being easy to install and maintain.

Grant currently has a few options that span many models and variations. Their main oil boiler is the Vortex Pro. It’s available as a system, regular or combi boiler and each boiler type is available as an internal or external unit.

This range of model variants ensures Grant has an oil boiler solution for almost any domestic property.

Best Selling Grant Boiler

Grant Vortex Pro Combi - Grant vs Worcester Oil BoilerGrant Vortex Pro Combi 26

Grant’s Vortex oil boilers have some of the highest efficiencies available in the UK for oil. They achieve seasonal efficiencies of up to 94.5%.  The range is available with heating outputs from 15kW to 70kW. They are:

  • ErP ‘A’ rated
  • Slimline models available, including the Vortex Pro Combi XS
  • All of Grant’s oil boilers incorporate their patented stainless steel heat exchanger technology, which ensures each product is highly efficient
  • The Vortex Pro range have a 10-year warranty.
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Worcester Bosch

Worcester Bosch was established in 1962 by Cecil Duckworth as Worcester Engineering Co Ltd.  Bosch acquired it in 1992, hence the name of the company today, i.e. Worcester Bosch. They manufacture a wide range of boilers, including gas and LPG, as well as oil.

Worcester Bosch currently makes the Heatslave II and Danesmoor models for properties with oil. There are a number of options for each, but the best-selling option is the Heatslave II.

Best Selling Worcester Bosch Oil Boiler

Worcester Bosch Heatslave II - Grant vs Worcester oil boilers | BoilerhutWorcester Greenstar Heatslave II Oil combi boiler

Suitable for small, medium and large-sized properties, this boiler features easy access connections and a one-piece stainless steel primary baffle and cross-firing burner. A Heatronic 4i digital control unit provides accurate control and diagnostic information.

  • Cross-firing burner
  • One-piece baffle for quick and easy servicing
  • Easy access oil and hydraulic connections
  • Digital control offering precision heating and hot water control
  • Lightweight aiding installation
  • Front access for routine servicing, including a pivoting expansion vessel for ease of access
  • Compatible with our Greenstar Comfort controls
  • Compatible with solar thermal
  • 7-year guarantee on Worcester primary heat exchanger
  • 80/125mm room sealed flues with lengths of up to 8m available
  • Plume management of up to 5m with conventional and flexi-flue kits also available
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Grant vs Worcester Bosch Comparison

It’s always hard to compare manufacturers because there are always differences that are hard to compare. But we’ll try. Above were the Heatslave II and Vortex Pro. Both internal floor-mounted combi boilers.

Both boilers can use renewable energy sources like solar energy and biomass. So you don’t have to depend entirely on oil to heat your home. Below is a side-by-side comparison sheet for both boilers.

BrandGrantWorcester Bosch
ModelHeatslave IIVortex Pro
Model Variant18/2526
Maximum Heating Output26kW26kW
Maximum Hot Water Flow Rate17 litres/minute18 litres/minute
Dimensions (mm) HxWxD860 x 614 x 606855 x 520 x 600


Please note the prices given below are for boilers only.  The final price for a boiler installation will include labour, chemical flush, magnetic and limescale filters, thermostats, etc.

Worcester Greenstar Heatslave II 18/25 – £2,990

Grant Vortex Pro Combi 26 – £3,033

Although the difference is negligible, the Grant boiler is still the clear winner here.

  • It is more energy-efficient.
  • It uses a stainless steel heat exchanger. Compared with aluminium in the Worcester Bosch. Stainless steel is more durable and highly corrosion-resistant. This is why manufacturers using them (Viessmann and Grant) can offer longer warranties.

The Grant oil boiler is fantastic value for your money.

Energy Efficiency

nergy efficiency has been a significant talking point for years now. Often, our customers will opt to pay more upfront for a higher-efficiency boiler.

This will save you money on your heating bills every year. Not only this, it will reduce your carbon footprint.

Grant beats Worcester Bosch in this area, but only just. The Grant is 93% efficient and the Worcester Bosch is 90%. This isn’t a huge amount, but it does add up. That’s £3 saved in every £100 spent.

Grant’s higher energy efficiency is down to their award-winning stainless steel heat exchanger. It has a larger surface area and low water content to improve the hot water performance of the boiler. Grant boilers also have a low-pressure cut-off switch, so the boiler will shut down if there’s water loss.

There’s another feature unique to Grant boilers. The Turbulator-Baffle system. This extracts the latent heat usually lost through the flue to be reused in the system.

How can Boilerhut help you?

Our job is to give you unbiased information.  The Grant oil boiler has come out on top in many independent reviews. We wouldn’t recommend a sub-standard product.

Furthermore, because of the long-term reliability and durability of Grant Oil Boilers, you get an extended 7-year parts and labour warranty, and the same is true of their stainless steel heat exchanger.

If you were to buy the boiler yourself and get it installed by a local plumber, you would only get a 2-year warranty. Find out more about Boilerhut oil boiler installation >

Get Your FREE Online Quote Today!
Save up to £590 PER YEAR on your heating bills.
Quote in 30 seconds. No obligation. Next Day installation.
Save up to £590 PER YEAR!

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