Your guide to boiler efficiency.

See how your boiler’s efficiency affects the environment and your wallet.

Boiler efficiency.

What is boiler efficiency?

Boiler efficiency lets you know how much of the fuel that’s used to power your boiler is converted into usable heat in your home. The higher the efficient rating of your boiler, the less wasted energy you’ll have and the less money you’ll need to spend heating it.

Older boilers often don’t stand-up to today's standards and regulations which means that they’re less energy efficient than modern boilers.

We’ll show you how to check your boiler’s efficiency and what the ratings mean.

How much can you save by replacing your old boiler?

The Energy Saving Trust has looked at how much you could save on your fuel bill in a gas-heated home when you replace your old gas boiler with a new A-rated condensing boiler:

Old boiler rating












Old boiler rating












Old boiler rating












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So for example, if you removed an E-rated non-condensing boiler and had a combi boiler installed in a semi-detached house, you could save £260 a year.

How do I check my boiler’s efficiency rating?

For all new boilers (those made since 2015), you’ll need to find the Energy-related Products rating (ErP rating). This is normally on the boiler itself and can also be found on the paperwork you got when it was installed.

If your boiler was installed before then, it may have a Season Efficiency of a Domestic Boiler in the UK rating (SEDBUK rating) on it.

If you can’t find either of those then you can check the model number of your boiler against the PCDC database and it may be able to tell you your boiler’s efficiency.

What is the ErP rating?

The Energy-related Products rating is a directive from the European Union and designed to encourage manufacturers to reduce harmful emissions and meet specific energy-saving criteria.

The ErP directive uses letters from A-G to rank the efficiency of a boiler or heating system, with A+++ being the highest rating and G rating being the lowest.

To give you an idea of the scale, A-rated boilers are 90% or more efficient, whilst G rated boilers are less than 70% efficient.

ErP rating diagram.

What is SEDBUK?

SEDBUK is another way of rating energy efficiency in appliances. There are two types of SEDBUK ratings:

  • SEDBUK 2005

  • SEDBUK 2009

SEDBUK 2005 uses letters, similar to ErP. The ratings go from A (the most efficient) to G (less efficient. SEDBUK 2009 uses percentages. The higher the percentage, the more efficient the boiler. A C-rated boiler for example would be 82-86% efficient, whereas an F-rated boiler would be 70-74% efficient.

SEDBUK was replaced in 2015 by the ErP ratings.


Get warm and cosy and save up to £540 on your annual gas bill^.

Plus if you’re an E.ON Next customer save £150 when you buy a boiler through E.ON. T&Cs apply.

Get a new boiler

Are condensing boilers more energy efficient?

Condensing boilers are designed to heat up your home and water as efficiently as possible and it’s a requirement that every new boiler must be condensing and have an A efficiency rating.

The difference between condensing boilers and non-condensing boilers is the amount of heat that they produce and that condensing boilers achieve over 90% energy efficiency.

How do I know if I have a condensing or non-condensing boiler?

If you’ve moved into a new property and you’re not sure if you have a condensing boiler, there are a few ways you can check:

  • Check the install date of your boiler. If you got a new boiler after April 2005 then the regulations will mean it’s condensing.

  • If your boiler has a metal flue then it’ll probably be non-condensing. Condensing flues are usually through an external wall or your roof.

  • If you see steam through an external wall or your roof and a white plastic pipe leading to a drain, then it’s most like a condensing boiler.

Why choose a Worcester Bosch boiler?

They’re fast and economical to run.

Worcester Bosch boilers are A-rated for efficiency, guaranteed to be 94% efficient, helping you to reduce your energy bills.

Smart connected thermostats.

Control your central heating and hot water with the wireless Bosch EasyControl, plus get easy-to-understand graphs on gas consumption and how efficient your heating programmes are.

Awarded Best Buy by Which?

Our new Worcester Bosch boilers build on the award-winning Greenstar range, offering smarter and more powerful condensing boilers with advanced technology to maintain water pressure.

Find out more about our Worcester Bosch Greenstar boilers.

^An average household could save up to £540 on their annual gas bill. Savings information for boilers in the UK provided by the Energy Saving Trust, based on a detached house with a boiler rating of G.