HeatingForce is reader-supported. When you buy through links on our site, we may earn an affiliate commission. Learn more

2021’s Best Oil Boilers [And A Complete Buyer’s Guide]

Considering a new oil boiler, and don’t know where to start? best oil boilers

Good news. Our 5-minute review of the best oil boilers covers everything you need to know.

We’re going to cover the best oil boiler brands as well as what size unit you need. We’ll also discuss warranties, price and even the cost of installation.


Choosing An Oil Boiler

Before reading this 5-minute review, bear in mind that different properties (even of the same size) have different heating and hot water demands.

Choosing the wrong boiler will mean one of two things:

  1. You’ve purchased a boiler that’s too big, paying extra for the boiler than you needed to
  2. Your oil boiler ISN’T powerful enough, so struggles to heat your house and hot water.

Those qualified to install oil boilers are OFTEC registered heating engineers. You can get multiple quotes and advice from them here.

It’s worth having them spec your property and they’ll determine which is the most suitable boiler to install.

Types Of Oil-Fired Boilers

When choosing an oil-fired boiler, it’s not just the brand you need to be considering.

Different heating systems REQUIRE a certain type of boiler. And, here are the three most common…


An oil combi boiler doesn’t require a hot water storage tank, cylinder or a cold-water tank. It heats water on demand.

The benefits here are that it’s a HUGE space saver not having these water storage facilities.

On the flip-side, they’re suitable for properties that don’t have high heating/hot-water demand (i.e. only one shower operating at once).


A regular oil boiler (sometimes called a heat only, or conventional) fills up a hot water storage tank, meaning it’s going to be suitable for heating systems where there is high hot water demand.

To feed to storage tank, there’s a cold-water storage tank (usually fitted in your loft).


System oil boilers work just like regular oil boilers. The difference here is that they don’t require a cold storage tank in your loft. That’s not just going to mean a reduction in installation cost, but it’s means one less thing that’s going to be repaired in the future.

If you live in a 4-5+ bedroom property and want to use 2+ showers at once, it’s advisable to go for a system oil boiler, over a regular.

Brands To Look Out For In 2018

There are a tonne of brands offering boilers. The problem? Most of them are mediocre quality, and over-priced.

At my time working in a plumbing merchant, most oil boilers were on an “order-in” basis. And, for the life of me, I can only remember ordering one of three oil boiler brands.

That’s not to say there aren’t other brands out there that are high quality. It’s just confirmation that homeowners like you, and registered OFTEC oil boiler engineers, like these three brands more than any other.

My opinion? If I was upgrading my oil boiler, I’d be making sure that I was sticking to these three brands.

The Top 3 Oil Boiler Brands


Let’s start this list with Warmflow. Warmflow oil boilers are the most efficient on the market. That’s not opinion; that’s fact! 

You’ll see plenty of manufacturers advertising their “A-rated” oil boilers. The problem? A-ratings are split between AA (the best) and A (the second best).

Warmflow produces the only AA-rated oil boiler in the UK & Ireland.

What does that actually mean? AA-rated Warmflows are up to 30% more efficient for hot water than some A-rated oil boilers on them market. And, that translates to drop in fuel bills, as well as doing your bit for the environment!

But, there’s something else we like about Warmflow. A brand’s boilers are only as good as the parts they use. And, the brands Warmflow uses for components are ones we know and love. This is what separates a oil boiler brand making this “top” list, to just being a cheap “no-name” brand.

Across their range, Warmflow use well known branded components such as:

  • Riello burners
  • Honeywell diverter valves
  • Grundfos pumps

We like 🙂


So, Warmflow are the most efficient boilers on the market. But, how does their warranty fair against leading brands? 

Well, it’s long. The warranty on their Titanium for instance, is 5-years. That compares to some Worcester Bosch oil boilers that only come with a standard of 2.

Another note here is that Warmflow offer an “out-of-the-box” 5-year warranty. As long as it’s installed by a qualified oil boiler engineer, that warranty is valid.

And that might seem normal, but it’s not. Other brands (Grant, for instance), only honour their 5-year warranty when the boiler is installed by their accredited engineers; you’ve been warned!

Warmflow Oil Boiler Range

And, Warmflow have an oil boiler to suit every property that’s located off the grid.


The U-Series is modern and stylish. It’s designed as an internal unit, fitting most kitchen and utility applications. And, the fact it’s easily accessible helps to reduce oil boiler service costs.


Struggling for space in your property? That’s where the K-Series comes into play; it’s Warmflow’s external oil boiler.

They’re quick and easy to install (reducing installation costs), and are fully insulated from the elements. If you need a boiler fitted externally; the K-Series is for you.


The B-Series has been designed for indoor installation, in areas such as boiler houses and garages. It’s got a highly efficient heat exchanger, and like the U-Series, easy access means reduced servicing time (and costs).

But it doesn’t stop there. Unlike cheap oil boilers, Warmflow have gone all out with the B-Series. They’ve fitted a Riello burner (the best in the business), meaning it’s not just efficient, but quiet too.


Grant offer one of the biggest and best range of oil boilers on the market. They’re an oil boiler specialist. 

They absolutely kill it with their Grant Vortex and VortexBlue, which boast ridiculously high energy efficiency levels (up to 93.3%) gross.


Their bragging rights don’t stop there.

When investing this amount of cash in your property with a new oil boiler, you want to make sure your back is covered, with a big warranty. Many of the cheap oil boiler brands offer little in terms of warranty(1-year) or no warranty, AT ALL!

No thanks.

Grant oil boilers, like the Vortex and VortexBlue? You’ll get a huge 5-year warranty when installed by an accredited engineer.

Oil Boiler Range

And, due to their extensive range, it’s not a case of finding the “most” suitable oil boiler for your property. Their range is so big; your oil boiler engineer will be able to find the EXACT grant oil boiler that’s perfect for your property. It includes…

  • Internal
  • External
  • Combi
Vortex Eco
  • Utility
  • External
  • Wall Hung (Internal)
  • Wall Hung (External)
Vortex Pro
  • Utility
  • External
  • Internal Comi

Worcester Bosch

Worcester Bosch need little introduction. They’re the most popular brand when it comes to gas combi boilers, and they’re just as popular in the oil boiler market too. 


Worcester Bosch oil boiler’s warranty starts at 2-years. Confirm with your engineer the exact warranty for the model you’re installing.

Typically, Worcester will increase a warranty up to 5-years during promotional periods, and when the boiler is fitted alongside other Worcester branded products (heating controls and boiler filters, for instance).

Oil Boiler Range

Like Grant, Worcester Bosch oil boilers come in all shapes and sizes. It’s definitely worth speaking to an OFTEC registered oil boiler engineer before deciding on a Worcester. They’ll be able to determine which is the most suitable Worcester oil boiler for your property.

You’ll be able to choose from their two ranges:

  • Greenstar Danesmoor
  • Greenstar Heatslave II

And, you’ll be able to install them:

  • Externally
  • Internally

Like Grant, you’ll be able to choose an oil boiler that’s a straight swap for your existing boiler in terms of kw output, but also:

  • Combi
  • System
  • Regular

Warmflow, Grant Or Worcester Bosch?

There’s no definitive answer here. Some installers (and homeowners) will prefer one brand over the other.

We’d be happy to fit any of the top 3 oil brands on our list. However, if you’re going for all out warranty, efficiency and therefore value for money; Warmflow is a solid pick.

Oil Boiler Installation Costs

Oil boiler installation costs vary considerably. The variation in price (depending on kw output and type of boiler) varies much more than it does with gas boilers. Typical purchases costs can be £1,200-2,000 with installation in the £1,200-2,200 range.

There’s more details on oil boiler installation costs here.

Oil Boiler Installers

For Gas and LPG boilers, fitters need to be registered with Gas Safe.

That’s not the case with oil. Fitters need to be registered with the OFTEC (Oil Firing Technical Association).

OFTEC are responsible for managing over 8,000 trade professionals in the UK. If your oil boiler installer isn’t registered with OFTEC, they’re not qualified to fit your boiler.

What’s Next?

Thanks for reading our 5-minute review of the best oil boilers in 2018, as well as the top brands, installation costs and the types of boilers you can install in (or outside of) your property.

Still got questions about oil boilers? Leave a comment below and we’ll do our best to help you out.



Avoid Expensive Breakdown Costs
Boiler Replacement Promise: If it's under 7 years old and we can’t repair it, we’ll replace it.
Try YourRepair. From £9/mo
All plans include: annual boiler service, all parts and labour, unlimited support and 24hr helpline.

Leave a comment

Your email address will not be published. Required fields are marked *


Fix things and tutorials

Get a Boiler on Finance

The best pay monthly packages available

Read guide
Heatable Boiler Replacement

Want a new boiler from HEATABLE?

Read guide
WarmZilla Boiler Replacement

Want a new boiler from WARMZILLA?

Read guide
Boiler Installation Costs

Confused about new boilers and their costs?

Read guide