Combi boilers

When a hot water tap is turned on or a room drops below a specified temperature, the room thermostat signals its connected combi boiler to fire up and pump hot water into the central heating system.

When BOXT installs your new combi boiler, you can expect:

• Step 1: The new boiler will be delivered on the morning of your installation.

• Step 2: The old boiler will be safely removed and disposed of.

• Step 3: The system will be flushed, then the new boiler, along with any new pipework, upgrades, and accessories, will be installed.

• Step 4: Your engineer will photograph each element of your new system to share with BOXT's internal auditing team for a comprehensive 61-point review.

• Step 5: Your engineer will demonstrate how to use your new boiler, as well as any additional accessories.

• Step 6: After signing off on the installation, BOXT will activate your boiler's warranty and upload all essential documents to the app.

As every home has unique requirements, there is no perfect one-size-fits-all boiler. However, BOXT's most popular combi boilers are:

• Worcester Bosch Greenstar 4000 25kw

• Worcester Bosch Greenstar 4000 30kw

• Navien NCB 300 30kw

• Vaillant ecoFIT Pure 830 30kw

To find your home's most suitable boiler, try BOXT's Find A Boiler tool.

Because combi boilers use the mains water supply to provide instant hot water, if more than one person needs to use a hot water outlet at the same time, they can struggle to meet the demand. If you have multiple people living in your larger home that will need to use multiple taps or showers at the same time, then a system or standard boiler may be a better choice. However as technology advances, more and more powerful combi boilers are being developed, so there may still be a combi boiler option that works for you. 

Combi boilers use the mains water supply to provide instant hot water on demand, which is very handy as you don’t need to wait for a hot water tank to fill before having a shower. However, it does mean they can struggle to meet demand if multiple people are using hot water taps or showers at the same time. If you use multiple bathrooms simultaneously, a system or standard boiler may be a better option for you. 

Yes, all modern boilers are required to be A-rated, meaning they’re at least 90% efficient. If you have an old boiler, you could benefit from big savings on energy bills by upgrading to a new combi boiler.

Learn more about boiler energy efficiency.

At BOXT we offer combi, system and standard boilers from a range of leading manufacturers including Worcester Bosch, Vaillant, Navien and Baxi. Using our handy Find a Boiler tool, in 90 seconds we’ll give you recommendations for the best boilers to suit your home, with a fixed-price including installation as soon as the very next day. 

The most common combi boiler problems are: no hot water but working central heating, no hot water and no central heating, and hot water only working when the heating is on.

Other issues may include boiler leaking water, thermostat error, loss of pressure, unusual noises, a frozen condensate pipe, cold radiators, and repeated boiler lockouts.

No, a combi boiler draws water directly from the mains water supply and heats it on demand, eliminating the need for water storage tanks.

To get the best out of your combi boiler, BOXT's experts recommend:

• Avoid keeping the central heating on 24/7

• Using a smart thermostat

• Adjusting the boiler controls

• Use thermostatic radiator valves

• Regular boiler servicing and system water treatments provided by a Gas Safe engineer

If you have a small home or flat and have relatively low water usage, then it's worth considering upgrading your boiler to a combi. They're compact, highly energy-efficient, and can help lower both your annual bills and energy usage.