Thanks for taking time to post the owner's manual link. We did save the original paper owner's and installation manuals. Unfortunately neither cover any troubleshooting instructions.

I thought hydraulic fluid level might have been low but removal of the vent cap at the tank showed fluid within 1-1/2" of the top. The manual calls for fluid within 1" of the top. I added some ATF and ran through the air venting procedure but still no movement at the cover.

There is an over pressurization safety bypass that might be stuck open. I have no idea how to safely test the switch though. Aquamatic will be open again next Tuesday. I will give them a call then and report back here with any updates.

Happy swimming season,

Joe Menacker