There are 5 ‘varieties’ of combi boilers:
The Combi Boiler (also known as an instantaneous boiler) is the No. 1 choice for UK homeowners. Its popularity is born out of its efficiency of directly heating the incoming mains cold water supply to the sanitary fittings within your home. Convenience and bliss!
Instantaneous Condensing Boiler
A higher efficient version of the Combi Boiler is the Instantaneous Condensing Boiler, which as the name states operates as an ‘instantaneous’ boiler. The upshot being, less energy usage for the same desirable hot water and comfort heating.
Combi (Storage) Boiler
A variation to the Instantaneous Combi Boiler type is the Combi (Storage) Boiler, which is designed to provide a higher performance due to the internal storage of heated water. The water storage facility generally provides higher initial water supply from cold water mains when first turning the tap on the sanitary appliance. Once the stored heated water has been completely drawn and depleted, the boiler will effectively operate as an ‘Instantaneous’ Combi Boiler.
Efficiencies will be dependent on the boiler make and model and water storage capacity.
Combi (Storage Condensing) Boiler
This type effectively operates as the ‘storage’ boiler type with at higher efficiencies for the homeowner.
Combined Primary Storage Unit (CPSU)
This special type of storage Combi Boiler has a very large water storage facility, allowing for high water flow rates to sanitary fittings and draw-off points. Furthermore, flow rates to radiators is higher and achieved before the water storage is fully utilised.
In essence, Combi Boiler means hot water on-demand from a space saving installation.