System boilers
Fixed-price system boiler installations
Get a new system boiler installed next working day¹, with flexible finance options available². Plus, get a free Hive Thermostat Mini with code FREEHIVEMINI*.
We'll beat any like-for-like price
UK's most trusted boiler installers
One year workmanship warranty on every installation
Popular system boilers
Worcester Bosch Greenstar 4000
The Greenstar 4000 comes in a range of outputs so it can efficiently power different sized homes
Worcester Bosch Greenstar 30i
Featuring a low energy pump, it helps to save on electricity bills too, alongside simple to use controls so you can easily stay on top of your energy usage.
Vaillant ecoFIT Pure 618
A modern and energy efficient boiler that will help to reduce your energy bills.
Vaillant ecoFIT Pure 625
A great choice and amazing value as an energy efficient boiler.
Benefits of a system boiler
Strong water pressure
System boilers use the mains water supply, so you'll get high water pressure.
Hot water from multiple taps
You can run multiple taps and showers without affecting your water pressure.
Economical
Quick to respond to your needs, especially if the tank is well insulated.
Upgrading a system boiler to a combi boiler
If you want more space in your home and currently have a system boiler which has a hot water cylinder, swapping to a combi boiler could help free up some space.
Use the BOXT boiler recommender tool to find your perfect new boiler. Answer a few questions based on your home and needs, and we'll give you recommendations for suitable new boilers, whether that's a system, combi, or conventional boiler.
If you choose to upgrade your system boiler to a combi boiler, we'll give you an instant online fixed price and a time estimate for your installation duration.
What happens when a system boiler is updated to a combi boiler?
- The existing heating and hot water system will be drained.
- The old or existing boiler and tanks will be removed, along with any old controls/thermostat.
- Your system will be converted to combi, which can sometimes take an extra day.
- The new combi boiler and filters will be installed.
- A chemical flush will be performed on the whole system.
- Smart thermostats will be installed and configured to the new boiler.
- You'll be shown how to use your new boiler and smart thermostat.
- All BOXT installs are post-checked by an expert before being signed off.
System to combi boiler reviews
System boiler brands
We stock a range of top boiler brands. Find your new A-rated boiler online with BOXT today.
Learn more about system boilers
What is a system boiler?
Like standard boilers, system boilers are usually found in larger homes with greater hot water and heating demands.
Unlike standard boilers, system boilers are filled directly from the cold water mains and are connected to a sealed system. This means there's no need for feed or expansion tanks in the loft.
System boilers are usually connected to unvented hot water cylinders and provide better hot water performance when simultaneously supplying multiple taps and showers.
System boiler FAQs
More boiler guides
Get a new boiler with BOXT
*Saving of £173.55 based on the Ofgem medium annual gas consumption of 11,500 kWh at the October 2025 UK average unit price of 6.288 pence per kWh including VAT. Emissions saved per year: 508 kg CO2 (0.184kg per kWh). Actual savings will vary depending on individual circumstances. Terms and conditions apply to Free Hive Mini promotion.
¹Next working day installation when you order before 3pm, subject to availability.
²Finance available subject to status. Click here for more information.
BOXT Limited is authorised and regulated by the Financial Conduct Authority. FCA register No. 767308. Finance is offered through HomeServe Finance Limited (FRN 994955) and in some cases we also lend with Propensio Finance Limited (FRN 806409). Finance available subject to status, affordability and a credit check. Terms and conditions apply. BOXT Limited acts as a credit broker and is not a lender. Registered in England & Wales company No. 08086606 VAT No. 257059782. BOXT Limited, 3320 Century Way, Thorpe Park, Leeds, West Yorkshire, LS15 8ZB.
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