The heart of your heating system – arguably of your home – is the boiler. This largely unsung hero works away quietly (alright - not always quietly) in the corner, keeping you and yours warm all year round. But when the utility bills come and they’re bigger than you expected, could your trusty boiler be to blame? Is it using too much power? Modern boilers have become steadily more energy efficient over the years, but they can run into trouble, especially if they’re not looked after. And if you have an older model, this may well be impacting your bills.
What’s a combi boiler?
The combination – or “combi” – boiler was first introduced to the UK in 1971. Unlike conventional boilers, they took water straight from the mains so they weren’t tied to a large tank in the loft. This made them compact, and – excitingly – allowed them to provide hot water almost instantaneously. They were also considerably more energy efficient than regular boilers. In the decades since their introduction, combi boilers have grown in popularity to the point where they’re now used in 70% of UK homes.
Regular or conventional gas boilers are still in use in many houses, as they still have a few advantages over combis. For example, they can send water to lots of taps without the flow getting weaker. This makes them more suitable for larger spaces or houses with multiple bathrooms. Modern conventional boilers can even be more energy efficient than a combi in the basic task of heating water, but they tend to lose heat through the hot water cylinder. So combis are probably still more efficient overall.
How does my combi boiler work?
When you turn on a gas-powered, combi boiler, a pipe at the bottom feeds gas from the mains through a valve into a combustion chamber, where it's set alight. The gas flames warm a heat exchanger which in turn heats cold water, which is then carried around your house and through the radiators. In a closed system, the same water circulates in a continuous loop. By the time it returns to the boiler, it has cooled, and needs to be re-heated. This is why the boiler needs to run continuously when you want the radiators on. Exhaust gases generated in the process are released through a flue pipe and out through a flue.
In 2005, the UK government made it mandatory for all new or replacement boilers to be condensing boilers. The clever thing about a condensing boiler is that it manages to retain and re-use some of the heat previously lost in exhaust fumes. This makes them up to 25% more efficient than older combi boilers.
How energy efficient is my boiler?
You don’t have to guess how efficient a boiler is – it should be written right there on the front. All boilers in the UK are required to have a Seasonal Efficiency of a Domestic Boiler in the UK (SEDBUK) rating. Using a scale from A to G, with A being the most efficient, SEDBUK indicates the average annual efficiency of any given boiler. The rating takes into account several factors - including boiler type, the kind of fuel used, and typical domestic usage patterns – to give you a pretty good idea of how efficient that boiler is. All new boilers installed in the UK must be A rated.
If my boiler’s so amazing, why is it pushing up my bill?
Well, you could have the wrong kind. While a combi boiler is suitable for most smaller homes, it may not be suitable for larger homes with multiple bathrooms or those with low water pressure. You can get a lot of advice online about the right size and type of boiler your home might need.
Or, if you’re living in an old property, you may have an older boiler. These are far less energy efficient than modern ones, and can develop faults that could easily inflate your bills. For example, a broken thermostat or a faulty motorised valve could cause the boiler to keep running when it shouldn’t be. Many older boilers are ignited by means of a pilot light, a small flame that burns 24 hours a day, and this alone will cost you a few quid extra every year.
Is your boiler running as efficiently as it could be?
If your energy bill is one sign that your boiler might be underperforming, another might be kettling. Strange noises from your boiler often mean nothing, but can sometimes indicate a problem. You may have a build-up of limescale on the heat exchanger, which could be restricting the flow of water through the pipework, causing your boiler to overheat and make those kettling sounds. If the boiler has to work harder to push water through pipes narrowed by limescale, it will use more energy.
Kettling could also suggest a build-up of sludge, which is caused by corrosion in the heating pipes. As well as potentially restricting water-flow, sludge can also attack internal components in your boiler. If left unchecked, corrosion damage could mean you have to replace the boiler altogether.
If you’re concerned about your boiler there are a few simple DIY checks you can make yourself before calling out the professionals. If you do have to call someone, though, make sure they’re a registered Gas Safe engineer.
If you’d like to make sure your heating system is well-maintained and that you’re protected should things go wrong, you could take out boiler cover.
If you want to find out more about boilers, have a look at our Big Boiler Handbook.