I use my prssure washer just a few times a year and always give it a shot of Pump Saver when I'm done. I'm not sure what the chemical makeup is but it boils down to a corrosion preventer and seal lubricant. I recommend it. Some also cycle RV antifreeze through the pump to accomplish the same thing. Pick it up at a bog box, comes as a spray can with a screw to the pump inlet fitting.

If you left the engine running over 2 min's without using the pressure wand, heat builds up and pop's the valve, supose to allow cool water to flow and prevent damage to pump.sounds like damage was done or something hanging up the unloader? If it's your fault, taking it back to anywhere, just adds to the cost of the next years machine/s retailers don't lose $$ they just past the cost of doing business on to the customer.

I messed with one of those, a gift from somebody, in the trash, but never got pressure up, so now, it has been waiting for 2 years for me to come get it out of the trash dump! I know, not much help. Folks have complained about that problem, but i never got one to work again.

Engine make would be a big help. Would you happen to have one of the newer Subaru's. If your model has the Subaru engine. It would be best to take it back to the dealer and let them get it going. For the new Subaru engines that are being put on some power equipment is so new that no one has much experience with repairing them. Sure they can go by the seat of the pants guessing. But that is all they will be doing and may cause more damage than good.