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How to Make a Combi Boiler More Efficient

Living in the unpredictable climate of the UK, many households rely on their central heating systems to keep warm. However, while using your central heating may cost more than you’d like, there are ways to make your heating system more efficient.

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Living in the unpredictable climate of the UK, many households rely on their central heating systems to keep warm. 

However, while using your central heating may cost more than you’d like, there are ways to make your heating system more efficient.

How efficient is a combi boiler?

Many modern combi boilers come with an efficiency rating of 98%, making them extremely energy efficient compared to other types of boilers. 

Combi boilers are A-rated, meaning that you can potentially save money on your heating bills and reduce your overall carbon footprint.


Is a combi boiler or system boiler more efficient?

How energy efficient a combi or system boiler is in your home, will really depend on how big your home is. 

System boilers take cold water from the mains supply, and then it is heated by the heat exchanger which transfers the energy from the gas to the water. This makes them ideal for homes which have a high demand for hot water. 

For smaller homes, usually with only one bathroom, a combi boiler would be the most energy efficient option. You will have an instant supply of hot water from a highly efficient unit that will help you to save money on your energy bills.

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What capacity combi boiler is most efficient?

What boiler capacity is the most efficient for your home will depend on several factors. The main things you need to consider when calculating the optimal capacity are the size of your home, the number of bathrooms you have and the number of bedrooms. 

For example, in a standard 3 bedroom home containing a bath, shower and up to 10 radiators, a great energy efficient choice would be a 24kw boiler. 

However, it’s not just dependent on the size of your home and how many bathrooms you have. A good heating engineer will be able to calculate the correct size of boiler for your home by carrying out a series of checks, which includes checking the flow rate of your incoming water mains. 

This is why it’s always a good idea to have someone attend your home to carry out a full survey. It’s also good for getting a feel for the company you might choose to change your boiler.

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What is flow temperature?

Flow temperature refers to the temperature of the water in the supply pipe of a heating system. 

The hot water is distributed via the pipework, and most of it is directed to radiators. The rest of the water makes its way to other facilities in the home where the water is used directly, like showers and taps.

You might have heard that reducing the flow temperature on your combi boiler will help to make it more efficient and in turn, save you energy and reduce bills. Reducing the flow temperature on your combi boiler could make your combi boiler run more efficiently and help you to save energy.

You should only turn down the flow temperature on combi boilers. Most traditional heating systems are set up to run at 80 degrees, but they can operate at a lower temperature.


How do I set the flow temperature on my combi boiler?

The exact steps to change your combi boiler’s flow temperature will vary from model to model and brand to brand. However, in general, the flow temperature can usually be changed by one of the following:



Your combi boiler may come with one or two dials that can be used to adjust the temperature. More often than not, your boiler will have two dials. 

One of these dials will change the heating temperature and the other is for adjusting the hot water temperature.

To change the flow temperature, you would use the radiator temperature dial. You may need to turn it to the halfway point to reach 60°C.


Digital displays

Certain modern combi boilers come with digital displays, which can make adjusting your boiler flow temperature a bit easier. For example, the Worcester Bosch 4000 and 8000 combi boilers both have a digital display. You can see a radiator symbol which indicates that you are in the heating mode of the boiler, and you can then use the temperature buttons to turn the temperature down to the required level. 

Your boiler may also have dials, in which case you will be able to adjust the flow temperature by turning the dial and viewing the settings on the digital display. 

Some modern boilers may have no dials at all, and you will be able to adjust the flow temperature using buttons on the digital display. These displays will usually feature + and – buttons that can be used to increase or decrease the temperature. 


Will changing flow temperature change how warm my home is?

Changing the flow temperature of your boiler to the recommended 60°C may change the temperature of your home. 

Reducing the flow temperature means your radiators will be colder to touch and it will take slightly longer for your home to heat up when the radiators initially turn on.

You need to experiment with the flow temperature on your boiler over a period of a few days to find a temperature that suits your home and occupants. You need to find a temperature that heats your home up at the speed you want and to the comfort level that you want.


What is the most economical setting for a boiler?

For modern combi boilers, the most economical setting for the flow temperature should be set anywhere between 60 and 70°C. 

If you want to have a good balance between warmth and efficiency, you will want to be keeping your boiler at around 65°C. 

For those who prefer higher temperatures, don’t set your boiler above 70°C. This can cause your boiler to become overworked and will likely reduce the overall efficiency, as well as the boiler’s actual lifespan


What temperature should my boiler be set at for central heating?

When it comes to central heating, the best range is between 18 and 21°C, since this is within most people’s comfort zones. 

For bedroom temperatures, try to keep it between 16 and 19°C. This is the most comfortable temperature for a good night’s sleep. 


Is it cheaper to keep a combi boiler on all the time?

Many people think that keeping their combi boiler on low all the time is cheaper than simply just putting it on when you need it, but this is a myth. Instead, it is much more energy efficient and cheaper to only switch your heating on when you need to. 

Constantly heating your home will not only result in energy being used, but also lost. In a standard home, heat loss is quite significant compared to the heat you’re putting into it through your boilers and radiators.

If you constantly leave your heating on low, your home may struggle to reach the desired temperature, meaning that energy will be used for long periods of time. 

Check out our guide for more detail on whether you should leave your heating on low all of the time.


What temperature should my boiler be set at in winter?

In the winter, your boiler should be set at around 65°C. Setting it a few degrees higher won’t hurt, but again, try not to exceed 70°C. 

Be aware of the type of people who live in your household. For example, if you live with elderly family members or have young children, your boiler temperature should not be below 60°C since it can increase the risk of illness. 


How to adjust the water temperature on combi boiler

As we’ve mentioned, your boiler will usually have two dials – one for the heating temperature and the other for the water temperature. Adjusting one will not affect the other. 

To change your water temperature, simply turn the dial to your desired temperature and then perform a thermometer test. You should be able to do this straight away. From here, you can keep making small adjustments until you’re happy with the temperature. 


Ways to make your combi boiler more efficient

Other ways that you can make your combi boiler more efficient include:


Having a programmable room thermostat or smart thermostat:

If you have a new boiler installation, this should be fitted as standard and your heating engineer will recommend a good control. This means that you can set your boiler for times when you are in your home, or you could even use a smart control app on your mobile phone to turn your boiler on and off or change settings.

If you don’t have thermostatic radiator valves on your radiators, it is worth investing in these as you can then adjust the room temperatures individually.

Have your combi boiler serviced annually:

As well as validating any warranty that you have on your boiler, a boiler service helps to keep your boiler running as efficiently as possible. 

A heating engineer will carry out various checks on your boiler and clean out certain components to ensure maximum efficiency. A boiler service is also useful for spotting any potential issues so you can call out the manufacturer. 

At Lacey Plumbing & Heating, we specialise in all kinds of domestic and commercial heating needs. 

If you have any questions or concerns about your combi boiler, or you are interested in having a combi boiler installed, feel free to contact our professional and friendly team.

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