All about me Combi Boost boosts the mains water supply to combination boilers up to 10 litres per minute. It sits directly on the incoming mains water & boosts water flow making it an ideal solution for properties with low mains supply. This inline pump should be installed directly onto the incoming mains using 3/4 BSP to 15mm or 22mm fittings either after the stop tap or before the boiler appliance Need to know. Boosts mains water flow up to 10 l/min. enhanced shower performance. Quicker bath fill. Stronger flowing taps. Flow indicator lights. WRAS Approved. Fittings kit available. 1 year warranty.