A less common system, storage combi boilers work like a combination boiler, but have an internal hot water cylinder built into the boiler. They are a good solution if you have a higher hot water demand but don't have the space for the separate hot water cylinder that a system or heat-only boiler requires. 

• hot water on-demand, but the hot water cylinder means hot water can go to several outlets at the same time without the pressure dropping (like it would with a regular combi boiler). 
  
• Takes up less space than a system boiler - the hot water cylinder is built into the boiler body, rather than being separate like a system boiler. 
  
• Cheaper to install than a system or heat-only boiler - as everything is built in, the unit is typically cheaper and is less expensive to install. 
  
• Solar thermal panel compatible - as it stores hot water, you can keep that water warm with solar thermal, which isn't possible with just a typical combi boiler.
  

• Take up more space than a combi boiler - due to the hot water cylinder built into the boiler's body. 
  
• System boilers can meet larger hot water demands - storage combi hot water tanks are typically sized between 40 and 200 litres, but some hot water tanks for system boilers can be 500 litres or more. 
  
• Less choice - being a less common type of boiler, there are fewer storage combi systems to choose from. 
• Engineer knowledge - being a less common type of boiler, some engineers may be less familiar with a storage combi boiler, making it trickier to repair or service.