Worcester Bosch Heatslave 15/19, No water pressure?

I realise that mains water is needed to increase pressure, but I can't see any valves or connections where i can loop a pipe in. The mains comes in the top to a service valve then to a flow switch and then into the water tank. Below there is a pipe going to a Tee to the pump and pressure gauge, no obvious means of adding the mains?