Homeowners Professionals

Is my boiler energy efficient?

Did you know that heating could account for around 55 per cent of what you spend every year on your energy bills? So, if you want to keep your household costs to a minimum, it makes sense to pay attention to the efficiency of your boiler. Older boilers become less and less efficient over their lifetime, which is why it’s recommended that you switch every 10 years or so. A new boiler will have an efficiency of around 90 per cent, but over 10 years this could drop making the boiler more expensive to run

By selecting the  right heating system  for your home, and making sure it runs as efficiently as possible, you could save yourself a lot of money in the long term. You will also be doing your bit to limit your carbon footprint and help the environment.

How can I tell if my boiler is efficient?

One of the easiest ways to check the efficiency of a boiler, whether it’s one you already have or one you’re thinking of getting, is to look at its efficiency rating. By law, all boilers must have one of these ratings. Since 2015, new models have been assigned ratings determined by the Energy related Products (ErP) directive. A is the most efficient grade while G is the least efficient, and boilers can be rated differently for their heating and hot water performance.

Before the ErP directive, boilers were scored on the Seasonal Efficiency of a Domestic Boiler in the UK (SEDBUK) system, which assigns them a grade from A to G and an exact percentage score. For example, an A-rated boiler will get an efficiency score of over 90 per cent, while a G-rated model will get a score of under 70 per cent.

Modern boilers should all have a good efficiency rating. This is in part because they are condensing models, meaning they capture some of the energy that would otherwise be wasted in the form of hot gases escaping from the flue. They use this captured energy to heat water returning from the central heating system. As a result, they don’t require as much heat from the burner, saving fuel and making them more efficient to run.

However, if you have an old model, you may well find that it has a poor efficiency rating. Because of this, you might be paying much more than you need to for your heating and hot water.

If you cannot find the efficiency rating, you can find out how efficient it is by checking its model number in the Product Characteristics Database (PCDB). You can usually locate the exact model number for your boiler underneath the unit itself, printed on a sticker. Have a look around the unit to see if you can find it. Once you have the exact model number, you can search the PCDB to find out how efficient it is. Remember that it will likely give you the efficiency rating from when it was new, so if you’ve had it for a few years, its efficiency will likely have decreased slightly.

What is the most energy efficient boiler?

The most energy efficient boilers you can buy are those that have an energy efficiency rating of at least 90 per cent. In fact, Viessmann’s  Vitodens 100-W combi boiler  is between 92 and 94 per cent efficient.

But sometimes it’s not just about the model of the boiler. The fuel and type can also affect the efficiency of your home, depending on how you use your boiler. If you’ve decided it’s time to replace your existing boiler with a new one, you’ll no doubt want to make sure you get a highly efficient model. However, it’s important to be aware that there is no single best solution for all households. The most energy efficient and practical boiler for your home will depend on a range of factors. Here, we break down what you should consider when you’re trying to find the right boiler for your property.


If you have access to mains gas, the cheapest and most efficient boiler for you will almost certainly be a mains gas powered model. This is guaranteed to cost you less than oil, LPG and house coal. If you’re not already on the mains, you may want to contact the company that owns the gas network in your area to see if it’s possible to get connected. Bear in mind that this company might be able to help you with the cost, and in some cases the work is fully funded.


While you can be confident that any new boiler you choose will be designed to be highly efficient, you should think carefully about the particular type of boiler you select for your home. There are three main types available. These are combination (combi), conventional and system models.

Combi boilers are highly popular, making up more than half of all new boilers being installed in the UK. Designed to be space saving because they don’t require a hot water cylinder or separate pump, they heat water directly from the mains, giving you hot water on demand. In contrast, conventional boilers need a cold water storage tank to feed a hot water cylinder. They are typically found in older homes and are often used when there is a high demand for hot water or multiple bathrooms. They can also be a good option in areas where water pressure is low. However, they don’t deliver instant hot water. Instead, water must be preheated.

System boilers  operate in a similar way to combi models in that they heat water directly from the mains and don’t use a cold water storage tank. However, they do use a storage cylinder and they can deliver a constant supply of hot water simultaneously to any number of taps. They are also compatible with solar water heating solutions, meaning they can deliver lower energy bills, as well as environmental benefits.

When asking yourself which  type of boiler  will be most efficient and practical in your home, you’ll have to take into account how you use your heating and hot water, as well as the size and layout of your property.


Once you’ve decided on the type of boiler you want, you’ll need to pick a model. Make sure you pay careful attention to the energy efficiency rating. By selecting a highly efficient model, you stand to save yourself a considerable amount of money over the lifespan of the boiler. You’ll also be doing your bit to reduce your carbon emissions.

It’s important to research your options, and note that while it may save you a little money upfront, going for the very cheapest model available could actually end up costing you more overall if it is less efficient than alternative options. Bear in mind that if you are considering a storage cylinder, they also have an efficiency rating based on their heat retention and loss results.

How can I improve the efficiency of my boiler?

If you’re wondering how to improve boiler efficiency, it pays to bear the following suggestions in mind.

Invest in a newer, better model

When you’re dealing with an old, inefficient and potentially unreliable boiler, your best option may be to cut your losses and replace it with a  new model. By swapping an outdated design for new condensing boiler, you stand to make major savings on your energy bills. Also, you won’t have to worry about your heating system breaking down.

Know your heating controls

It’s not just the model of boiler you have that impacts on efficiency. How you use it will also have a bearing on costs. There are now a wide range of heating controls available that can help you to control your bills. Ideally, the complete set of controls for your system will include a boiler thermostat, a programmer or timer, a room thermostat and thermostatic radiator valves. By making sure you have these controls and getting to grips with how to use them correctly, you could significantly reduce your running costs. For example, turning your room thermostat down by just one degree could save you around £60 a year.

Ensure hot water cylinders are well insulated

If you have a boiler that uses a hot water cylinder, make sure this is well insulated. New models are factory insulated, but if you have an old one, topping up the existing insulation to 80mm could help you to save around £20 a year. Also, if you’re buying a new cylinder, make sure the one you go for is no bigger than you need it to be.

Use hydraulic balancing

Hydraulic balancing ensures that all radiators are supplied with exactly the amount of heat they need, and it can increase the efficiency of a heating system by as much as 15 per cent. The easiest way to do this is to call in a heating engineer.  

How much does a gas boiler service cost?

You can expect to pay anywhere between £60 and £170 for an  annual gas boiler service  depending on the size of boiler and style of unit, although typically prices range between £65 and £110. A number of factors can impact on how much you pay. For example, a one-off boiler service - as opposed to an annual service - may cost you more as it may involve more work.

The type of boiler you have, where you live and the company you use will also have an effect on price. You may be able to save money by comparing quotes from a few different engineers or companies, but always make sure you go for a Gas Safe registered professional.

If your boiler needs repairs, you will usually be required to pay extra for them. However, check if your appliance is still under warranty as some repairs might be covered by it. Also, some boiler repairs may be covered under your home insurance policy.

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