Is there a minimum flow rate for filling TankBoost?

No, there is no minimum flow requirement for filling the TankBoost. However, a restricted water main (i.e. lead) will increase the time taken to replenish the tank. If you have a poor natural flow of mains water into your property (less then 12L/min) you could use different products alongside TankBoost. For example, HomeBoost can be installed before TankBoost to boost the incoming mains water supply up to 12L/min.