Power Button and Home Button-->>Boot Loop

Hello to all!! My cousin's iPhone 6 was lying in water at the table for around 3 to 4 hours.After that the power button and the volume buttons doesn't work...the thing is that every time i open the flashlight app the volume buttons work properly...the power button doesn't work at all..I took out the motherboard and cleaned it but nothing new...the worst part is that when i press the power button and the home button for restart the phone stucks in boot loop... do you believe that the motherboard is damaged and needs to be cleaned in ultrasonic??