Combines 1660 Header keeps creeping down

I worked a 1460 a in Western Aus a few years ago with a 30 ft front and 5400hrs which did the same. Fitted a new hydralic pump, which stopped it. Hope it isn't that but it could be another possibility. Cheers Beltbreaker

It was the poppet valve. Surprisingly it was extremely easy to replace the poppet valve. Figuring out where it was took the longest time! It is right under the header raise and lower speed control bolt that sticks out of the hydraulic block about 4 or 5 inches. Took a allen wrench and got it off and replaced the o-ring, poppet valve, and spring and put it back together and wallah, the header stays right where I put it!!! Woohoo. We are harvesting wheat now. Things are going good *knock on wood*! I also replaced the front half of the rotor with Gordon Rotor bars and the new high profile rasp pads. lord willing, everything should go good. ;-)