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Witten by Bernard Morgan (Engineer).
First Published: January 24, 2018. Updated: November 16, 2023

Grant vs Worcester Bosch

Grant or Worcester oil boiler, which is the best oil boiler?

When you’re living off the mains gas grid, whether you’re in an urban or a rural area, Grant boilers 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 to run your central heating system on.  While there’s not an overwhelming option in the current market for oil boilers, you still have a good range to choose from when upgrading your oil heating system.

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 four decades now. Their range of oil-fired condensing boilers are very highly reviewed and heavily favoured above other brands by reputed review magazines and websites. Grant’s oil-fired condensing boilers range have a reputation for quality and reliability, on top of being easy to install and maintain. The Grant Vortex and VortexBlue oil boiler ranges are trusted by engineers and householders all over the UK.

In 2016, Grant sold more Vortex and VortexBlue oil condensing boilers than any other oil boiler brand in the UK (source: EUA).  And this year, in a 2017 Boiler Survey done by a prominent review magazine in the UK, all of Grant’s oil boilers were awarded a “Best Buy” award.

Grant has a wide variety of 63 oil boilers, consisting of internal, external, system, boiler house, wall hung, and combi variants. Consequently, Grant has an oil boiler solution for almost any domestic property’s heating needs. This kind of extended range of oil boilers wasn’t available to off-grid residents some years ago. But now, with so much choice on offer throughout the Vortex and VortexBlue ranges, Grant oil boilers have established themselves as market leaders. One of the best selling oil boilers from Grant Engineering is:

Best Selling Grant Boiler

Grant Vortex Pro 26 Floor Standing Combination Oil Boiler

Grant’s Vortex oil boilers have some of the highest efficiencies available in the UK, achieving gross seasonal efficiencies of up to 93.3% (SAP 2009).  The range is available with heating outputs from 12kW up to 70kW.

Grant has got a wide range of oil boilers that suit all types of houses, whether white cased utility internal models or powder-coated external models, to wall-hung boilers, to the red cased boiler house models.  Below are some of their key features:

  • ErP ‘A’ rated
  • Slimline models available including the Vortex Utility 15-21kW which is only 348mm wide, and the Vortex Combi XS which is 515mm wide
  • All Vortex and VortexBlue Combis come with a 24ltr expansion vessel as standard
  • All of Grant’s oil boilers incorporate their patented stainless steel heat exchanger technology which ensures each product is highly efficient
  • VortexBlue models have the same dimensions as Vortex equivalents so ideal for replacement boiler installations
  • All Vortex oil boilers are available with a 7-year guarantee when installed and registered by Boiler Hut Ltd (subject to T&Cs)
  • All VortexBlue oil boilers are available with a 10-year guarantee when installed and registered by Boiler Hut Ltd (subject to T&Cs)
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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.  Their current range of oil-fired boilers is around 30, and that includes internal and external models.  They manufacture a wide range of boilers, including gas and LPG, as well as oil.

Best Selling Worcester Bosch Boiler

Worcester Greenstar Heatslave II Oil Combination 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. The next generation 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
  • 5 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

As pictured and described above, the two comparable boilers for Grant and Worcester Bosch, in terms of performance, are the Grant Vortex Pro and Worcester Bosch Greenstar Heatslave II. Both these boilers are floor standing boilers meant for internal installation.

These boilers are recommended for small houses or apartments with about 10 radiators and 2 bathrooms. They can also 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.


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

Worcester Greenstar Heatslave II 18/25 Combination Boiler Oil – £2,320.96

Grant Vortex Pro 26 Floor Standing Combination Boiler Oil – £2,293.40

Although the difference is negligible, the Grant boiler is still the clear winner here. Let me explain why. Not only is it more energy-efficient, but it’s also got a stainless steel heat exchanger compared with aluminium in Worcester Bosch. Stainless steel is more durable and highly corrosion-resistant. This is why manufacturers using them (Viessmann and Grant) can offer longer warranties. Keeping that in mind, the Grant oil boiler is amazing value for your money.

Energy Efficiency

With threats like Global Warming and Climate Change looming, energy efficiency has been a major talking point for years now. Especially with modern condensing boilers now running at almost 94% efficiency. Installing a high-efficiency boiler not only saves you money on energy bills but also helps you leave a smaller carbon footprint. You are being kinder to the planet. Grant beats Worcester Bosch in this area, but only slightly. With 93.6% efficiency for the Grant oil boiler compared to 90.9% for Worcester.

Even though the difference isn’t massive, with all boilers in the market today so evenly matched, even a slight edge can make a difference. You do want to buy the best product possible for the money. Grant’s higher energy efficiency is down to their award-winning stainless steel heat exchanger with 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, which is the turbulator baffle system, which extracts the latent heat usually lost through the flue to be reused in the system. The recycled and reusable energy means higher energy efficiency for the boiler, which translates to even lower energy bills. And since both boilers cost pretty much the same, the Grant boiler with all these additional features is a steal!

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.  The fact that Boilerhut is Grant Approved Installers doesn’t factor into our recommendation.

We wouldn’t recommend a sub-standard product.  Furthermore, because of the long term reliability and durability of Grant Oil Boilers, you get extended 7-year parts and labour warranty, and the same on their stainless steel heat exchanger.

If you were to buy the boiler yourself and get it installed by a local plumber, you will only get a 2-year warranty.

Get Your FREE Online Quote Today!
Save up to £590 PER YEAR on your heating bills.
Getting a quote takes less than 2 minutes. No obligation.
Save up to £590 PER YEAR!

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