Marey 240V Electric Tankless Instant Electric Water Heater 6GPM 24kW ECO240

Marey 240V Electric Tankless Instant Electric Water Heater 6GPM 24kW ECO240 purchased from ebay seller (commercial_bargains) heater is weak at best and the 2.5 weeks it took to get a refund from seller in which they took 15% just cause they could. I called the manufacturer 2-3 times a day for a week. no answer at all!