We bought a home Lite GCV160 with a honda engine pressure washer last fall. I used through out the fall. Stored in warm garage/ no gas/ same oil. Changed the oil. Turned it on and the pressure wasn't same.I was losing water literally through a plastic pressure valve at the bottom of the engine. Please advise.

Hi,
Did you use soap in it and not flush it before storage? The residue will cause sticking. Restarting multiple times will often clear this; just takes time and patience.
The owners, parts and maintenance quick reference are on this page for downloading:
Homelite :: Product Owner's Manuals (http://manuals.homelite.com/documents/2554)
Probably only the first 20 pages of the owners manual are relevant as it is in three languages. Likewise the first three pages of the parts manual. And the first quick reference card is English. The would be the three items on the top row; they are pdf and the print screen in Adobe Reader will allow you to print only selected pages, though this is not the defaule and you will have to select it before printing.
Peace,
Clarke

You are losing water though the pump, not engine, This is one of the cheap models with a pump under the engine. This part goes out often and not using it, is one of the reasons. They often go bad just sitting.

The other main reason they go bad, if when you use it, you spray water, but then, stop spraying water, and leave the engine running.

These pumps are water cooled, and do not have any water bypass on them like the better units do.

If you leave them running without spraying water out the hose, for more than one minute it can easily damage the pump, if you let one run without spraying water for over 3 minutes it almost always does some damage.

We used to refer to these as disposable since the cost of replacing the pump was almost the same as buying a new engine.

But very likely you will have to buy a pressure/heat valve for the pump ( if that unit has a one that can be replaced)