Troy bilt pressure washer 2550 psi 6.25 hp. we borrowed from my brother and it doesn't have full pressure coming from the nozzle because there is water steadily coming out of the side from a sun shaped thing down low, i have to lay the washer on its side to see it. How do i stop water from coming out of there?

There is a valve installed to release water out of the system if water temp. rises to a level that may damage the pump. Water temp will rise when motor is running and you are not spraying water. This part is called a thermal valve. It can begin to leak water if worn out or debris under seat, however may not effect a lower pressure at the wand unless it leaks more water when you are spraying than when in bypass. You can see various thermal valves by searching on ebay with the key words :
"pressure washer thermal valve". Pressure is created at the tip of the wand. If the nozzle at the wand is worn or too large for the system, pressure will be reduced. You can check if the tip is correct by using a different tip that came with your system or using new of correct gpm as noted on the specs. of your system. Good luck