ErP Boiler Ratings Explained: Is Every New Boiler A-Rated?

In practice, yes: every new gas boiler you can buy for a UK home carries an A rating for heating on its ErP energy label. The rating tells you the boiler's seasonal efficiency under standard test conditions, which is why it barely separates one modern boiler from another. What makes a real difference to your bills is how the boiler is sized, set up and controlled in your home, and in England a replacement gas boiler also has to meet the Boiler Plus rules on efficiency and controls.

What is an ErP boiler rating?

ErP stands for Energy-related Products. It is the European energy labelling and ecodesign framework, still applied in Great Britain, that gives heating appliances a seasonal efficiency figure and a letter band, like the label on a fridge.

For a boiler, the key figure is its seasonal space heating efficiency: how much of the gas it burns ends up as useful heat over a typical heating season. That percentage is converted into a band on a scale that runs up to A+++. A combi boiler's label also shows a second, separate rating for hot water, with a letter band and a load profile, a code showing the size of hot water demand it was tested against. Most people only look at the heating letter, but for a combi the hot water rating is worth reading too.

Why are all new gas boilers A-rated?

Because ecodesign rules set a minimum seasonal efficiency that only condensing boilers can meet, and current condensing gas boilers land in the A band. In England, Boiler Plus sets the bar higher again for replacements.

A gas boiler cannot reach the plus bands on its own. Those are there for heat pumps, which deliver more heat than the electricity they use, and for combined packages. So an "A-rated boiler" is simply a modern condensing boiler, and comparing two new boilers by their letter tells you almost nothing. The seasonal efficiency percentage on the product data sheet is more useful, although the spread between reputable models is usually only a few points. The older SEDBUK bands, which also ran from A to G, are the ones you may see on older boilers and in older advice. "Condensing" describes how the boiler recovers heat, not whether it is a combi, system or regular boiler; all three types are condensing today.

What Boiler Plus adds in England

Boiler Plus is a set of rules for gas boilers fitted in existing homes in England since April 2018. It sets a minimum ErP efficiency of 92% and makes time and temperature controls compulsory.

Every replacement gas boiler must be fitted with a programmer or timer and a room thermostat, if working ones are not already in place. A combi boiler must also have at least one extra energy-saving measure from this list:

• Weather compensation, which lowers the boiler's water temperature when it is milder outside.
• Load compensation, which lowers it as the house approaches the set temperature.
• A smart thermostat with automation and optimisation, which learns how the home heats up and adjusts start times and temperatures.
• Flue gas heat recovery, a unit that recovers heat from the flue gases to pre-warm incoming water.

Because most boilers on sale already exceed 92%, the efficiency rule rarely limits your choice. The controls rule is where installations fall short. Building Regulations updated in 2022 also expect self-regulating controls, such as thermostatic radiator valves, in each room when a boiler is replaced, where that is reasonably practicable. Our guide to fitting a smart thermostat with a new boiler explains which controls earn their cost.

Does the rating match what you get at home?

Not automatically. A condensing boiler only reaches its rated efficiency when the water coming back from the radiators is cool enough for it to condense, and that depends on how it is set up.

Condensing happens when the return water is below roughly 55°C. A boiler left with its flow temperature turned high, feeding radiators that are too small or a system that is not balanced, sends hot water straight back and spends much of its time not condensing. It still works, but below its label. The simplest improvements are a lower flow temperature where the radiators can deliver enough heat, correct sizing so the boiler is not oversized for the house, and controls that let it modulate down rather than cycle on and off. Sizing is explained in our guide to sizing a boiler.

What controls do to the label: the package rating

An ErP label can also be produced for a package: the boiler plus the controls fitted with it, and sometimes solar thermal. Better controls add a few percentage points to the package figure.

Controls are graded into classes, from a basic on/off room thermostat up to multi-sensor systems and weather compensation, and each class adds a set bonus to the package's seasonal efficiency. That is why a boiler fitted with weather compensation or a qualifying smart control can carry a higher package rating than the same boiler with a basic thermostat. If an installer quotes a package rating, ask which controls it assumes and whether those controls are actually in the price.

How to use ErP ratings when comparing quotes

Use the rating as a floor, not a decider. Any new gas boiler you are quoted should be A-rated for heating; beyond that, spend your attention on sizing, controls and installation quality.

• Check the heating and hot water ratings on the actual model quoted, from the manufacturer's product data sheet.
• Check which Boiler Plus measure is included if you are having a combi fitted, and that it is named on the quote.
• Ask what flow temperature the boiler will be set to at commissioning, and whether the radiators allow it to be lowered.
• Ignore claims that one A-rated boiler will cut your bills dramatically compared with another. The gap between modern boilers is small; the gap between a well set up and a badly set up installation is not.

For what a complete quote should list, see comparing boiler quotes. If your current boiler is modern, working and already condensing, replacing it for a better rating alone is rarely worth the money; tuning its settings and controls may get you most of the benefit. If it is older and non-condensing, book a free survey and we will quote a correctly sized boiler with the controls it needs.