I have a Hayward DE filter with a side (Push - Pull) valve. While attempting to open the valve to backwash, the pinch pin attaching the handle to the piston broke. This has happened before and I've used a tool that's designed to remove threaded fittings on an underground sprinkler system to remove the piston. This time the piston will not move. A few months ago I replaced the O rings and lubricated them with Aqua Lube. Since then I had been opening the valve at least once a week to be sure that it would move. Unfortunately I had to be away for a month and now I have the problem. I think daily temperatures of over 100 may be a factor. The only action I can think of is to try heating the exterior of the valve with a heat gun to free up the O rings. Any other suggestions?