Hello Tuannmai. We are sorry to hear you're experiencing this issue. This product is covered by a 1 year limited warranty. Please contact our Customer Care Team at 1-888-412-6001, Monday – Friday, between 8 AM to 6 PM ET, so we can gather more information and proceed with troubleshooting. We hope you will give us the opportunity to help resolve the issue.
Your TotalPond Water Gardening Specialist, Mary