Troy-bilt used to be a very well respected name in equipment. They are not made even close to as well as there were just 12 years ago.
When Troy-bit vent out of busness about 9 years ago, Briggs and stratton bought the pressure washer company.
You are not going to like what I have to say very much, but when one of these inexpensive pumps stops working, there is very little you can do but either replace the pump or replace the whole thing. At some point in time there got some corrosion inside the unit. When this happens the first thing that goes bad is the presure relief valve. These usually cannot be replaced. Then the rest of the pump messes up.
Yes the could be rebuilt and then you would have about a 40% chance of it working, but the cost is as much as replacing the whole pump. These were meant as "Throw-away units"
Pump part number is: 202274GS ASSY, Pump
Here is the parts list for this model.
The distributor for Troy-bilt is Oscar Wilson in St. Louis.
You can go to their website and get in touch them. They can give you all the information you need.