How Efficient is my Boiler?

Finding the efficiency of your boiler

The first thing to do is to check your boiler for a little sticker with an energy efficiency rating on it. Most modern boilers should have this sticker either on the boiler itself, or somewhere in the pack that you will have been given. The rating will be clearly displayed on this.

If your boiler is older, or you just don’t have this sticker, then there are a few other ways to work out how efficient your boiler is.

The key is going to be working out the model number. Check under the boiler where the pipes come out, and under the flap at the front where the dials are. Usually there is a little sticker or plate with the exact model. This will mean a brand name, like Vaillant, Worcester Bosch, Ideal, Baxi or any number of others. Along with the brand there will be a model, usually this will be a number that refers to the size of the boiler and perhaps some other qualifiers, for example Worcester Bosch Greenstar 24i.

Once you have the model, the best place to check the rating is to go to the pcdb database. This database has nearly every boiler ever made and it’s really easy to find your boiler and get that efficiency figure. You can visit the site here.

The figure you are looking for is the seasonal efficiency, as this gives the fairest reflection of how the boiler performs over the course of a year.


What is a good rating?

So you’ve got the rating, but what does it mean? Well, the figure is going to range from 60% all the way up to 95% depending on the age and type of boiler. Any boilers manufactured today are going to be in the high 80s or low 90s, which are very efficient boilers. Anything under 85% is almost always going to be a non-condensing boiler and likely 15 years old or more. We would say anything above 85% is good enough, and we would not recommend changing the boiler until it stops working, as the paybacks would be very poor. Boilers below 80% are going to be those older models, and it may be worth switching these to a newer model of boiler; this will be very dependant on the property and the potential savings.

What about the letters? Well, the letters are just a better way to convey the efficiency figure. Anything below 70% efficient is G rated, and the rating goes up from there in 4% increments, with 82-86 being a C, 86-90 being a B and 90+ being A rated.


What if you can’t find your model number?

It might be that the boiler model number has worn off the plate, or you’ve lost the documentation the boiler came with. In this case it can be quite tricky to work out the efficiency. We can only really get a rough idea.

Your plumber will likely be able to give you the model number by removing the cover on the boiler and taking a look inside, but we would not recommend doing this unless you are a Gas Safe engineer. Instead we would suggest trying to check for some of the telltale signs of the type of boiler you have. Check to see if the boiler has a condense pipe running from under it. This will usually be a white plastic pipe next to the copper pipes where the water comes out. The pipe should go to a drain or even through the outside wall into a downpipe. If this pipe is present, then you have a condensing boiler of relatively high efficiency (i.e. above 85%).

>>>What Kind of Boiler Do I Have?<<<

You can also look at the flue. If you have an old open flue or the large ‘biscuit tin’ type flue, chances are the boiler is older and less efficient.


Just because you have an old boiler does not mean you should change it. For many, especially smaller properties, the savings to be made will be small and we would usually suggest waiting for the boiler to break down or become unreliable before replacing it. Every property is going to be a little different though, so seek advice from an independent company (not your heating engineer!).


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