Combi Boilers FAQ


Understanding the world of boilers can often be a difficult challenge with so many manufacturers, models and types of heating systems to pick from. We always try to make our sales and installation process as simple and clear as possible. To help, we've put together some of the most frequently asked questions and their answers. But if you're not able to find the answer you're looking for you can always get in touch with us to find out more.

What is a Combi boiler?

Combi boilers, or Combination boilers, are the most popular type of boiler in the UK. They're used by 74% of households.

They're named ‘Combination' because they combine a high-efficiency water heater and a central heating boiler all in one package.

Combi boilers are efficient and cost less in heating bills.

That's because:

They only heat water when you need it, rather than storing hot water up
They're small and compact, as they don't use an external hot water tank.

What is a combi boiler?

A combi or combination boiler is usually a small sized boiler that combines the function of heating your central heating and heating your water. It is often used in small properties where space is short and a smaller boiler is needed to fit compactly in a tight space like a kitchen cupboard.

How does a combi boiler work?

Combi boilers work by remaining in a constant state of standby. This means that when a water tap is put on they quickly heat the water and deliver it to the tap hot. This is ideal for households that want to reduce the energy and cost inefficiency of having the heating system constantly on.

How much is a combi boiler?

The cost of a combi boiler depends on a number of different factors such as manufacturer, power output, size and the size of your central heating system. At BOXT we're able to provide you with a quote in 90 seconds whilst also making sure that we pick the right boiler for you. We do this by asking a number of questions about your home such as how many bathrooms the property has, the positioning of your flue and how many bedrooms are in your house.

What size combi boiler do I need?

When you choose a combi boiler there are a few considerations to take into account regarding the size. Firstly, you may want a combi boiler to fit into a tight space, so you should take note of the boiler dimensions and measure whether it will be able to fit. However, it is vital that if you are looking for a boiler based on physical size that you make sure the boiler has a strong enough output that it can warm your home. As part of the questions we ask when we give you a quote, we ask about the size of your home, ho wmany bedrooms you have and how many bathrooms are on the property. The answers to these questions will help us determine how powerful your new combi boiler needs to be.

How long does a combi boiler last?

There is no right answer for this question as each and every boiler is entirely different. The lifetime of a boiler depends on how it was installed, how it was maintained and how it was used. There are plenty of high quality boilers that can last for over 30 years. However, it is generally agreed by multiple industry sources that the average lifespan of a boiler is 10 - 15 years. This is likely to be less if the boiler hasn't received regular servicing and proper maintenance from a professional boiler engineer. However, BOXT protect the majority of our boilers with a 10 year warranty in order to ensure if something does go wrong, you can rest assured that you want be out of pocket to fix the problem.

What is the best combi boiler?

At BOXT we don't believe that any particular boiler is best as there are a number of factors that will influence a boilers suitability for a property. However, we strongly advise customers that our Worcester Bosch combi boilers are some of the most reliable, energy efficient and cost-effective boilers that many homeowners can buy. Worcester Bosch regularly appear top in independent Which? boiler assessments and most of our Worcester Bosch boilers come with 10 year guarantees.

What temperature should hot water be set at combi boiler?

The temperature should be set to your own personal preferences, which obviously differ from person to person. Most combi boilers have seperate temperature controls for the hot water and central heating system. If your boiler has two dials then you should aim to set the central heating control to circa 80°C whilst your hot water control should be set to meet your hot water requirements at a temperature between 55°C and 60°C.

Should a combi boiler be on all the time?

It depends on whether you're in the property all day. If you're not, it may be more energy efficient to schedule the central heating system to be turned off during the day when the property is empty. However, you may wish to program the heating to be on all day during the weekend or during the colder winter months.

Why does combi boiler drop pressure?

If your combi boiler is losing pressure (either suddenly or slowly over a period of time) it could be due to a leak on your central heating system. Sometimes these leaks aren't obvious and can't be seen because they are happening under floorboards.

What's the difference between combi boiler and condensing?

A combi boiler remains in a state of constant standby and doesn't require a water tank. Instead, when there is a demand for hot water, it quickly warms the water to a high temperature. Condensing boilers use the same technology but instead reduces the heat from flue gases, conesing the vapour produced by the boiler. This means that the energy efficiency tends to be slightly better.

What are the benefits of a combi boiler?

Combi boilers are incredibly energy efficient and affordable to run as the boiler system only activates when there is a demand for hot water. This can lead to reduced heating bills.

A combi boiler doesn't require a water tank so is often small enough to fit into small properties and into the tightest spots such as kitchen cupboards.

A combi boiler can be more environmentally friendly due to its high energy efficiency rating.

What is the smallest combi boiler available?

The Worcester Bosch Greenstar 28CDi Compact is one of the smallest boilers available in the UK measuring just 39cm wide, 28cm deep and 69cm in height. Despite its size it's capable of heating 11.4-litres of hot water per minute.

What is the best combi boiler for a large house?

The Worcester Bosch Greenstar 42CDi Classic is the gold standard of our boilers and ideal for heating a large house or residential property. Capable of heating 17.2-litres of hot water per minute, the 42CDi Classic is reliable, long-lasting and comes with an impressive 10 year warranty to provide peace of mind.

Do I need a water tank with a combi boiler?

No. Combi boilers don't require a water tank as they work by heating the water on demand. This means that combi boilers are energy efficient and often more affordable in running costs.

How much does a combi boiler cost to run?

The cost of running a combi boiler tends to be very affordable because the system only heats water on demand as supposed to remaining on constantly to heat a water tank. However, the running costs depend on factors such as the boiler's manufacturer, energy efficiency rating, how long it's been programmed to be on for, the level of hot water usage, the preferred temperature, size of house and even the local climate.

Can a power shower work with a combi boiler?

In general, a power shower requires a pump and water tank to function. Because a combi boiler doesn't require a water tank, your shower would take it's water pressure from the mains.

How much to replace a combi boiler?

Costs for replacing a combi boiler depend on the hot water demands of your home, the cost of your new boiler and installation. At BOXT we provide one simple low-cost quote in 90 seconds with everything included. No upsells, no additional costs.

How to use a combi boiler efficiently?

You can ensure that your combi boiler runs efficiently for energy and cost by programming your thermostat to keep your heating system at your preferred temperature when you're home. If you work during the day and your home is empty, you may want to reduce the temperature or have the heating system turned to a lower setting during this time period. It is advised to not turn your heating system entirely off as more energy is required to bring your boiler up from zero. Alternatively, you can set your thermostat to automatically turn off when the room temperature reaches the optimum temperature to avoid the heating system from being constantly on.

Are combi boilers noisy?

Whilst no boiler is ever going tobe virtually silent, a noisy combi boiler could indicate there is an underlying issue with the boiler or central heating system. Having your boiler regularly maintained and serviced will ensure that any boiler issues can be identified and rectified before the issue becomes too large to tackle.