My Backwash Valve Won't Shut Off - My Back Wash Valve Leaks from the Top - My Backwash Valve Leaks Around the Shaft - My Backwash Valve leaks from the Housing.

    There are a number of places where a backwash valve can leak. There are 2 types of backwash valves:
        Push Pull Back Wash Valves and Dial Valves can leak from the same areas:
            1.) Around the S.S. shaft as it goes through the top of the valve assembly.
            2.) From the Back Wash Valve Outlet (It is flooding my yard.)
         3.) From the lid / top of the backwash Valve (Not from the shaft, but the top cover where it attaches to the Valve housing.)
         4.) From the housing Itself
         1.) My Backwash Valve leaks around the S.S. shaft as it goes through the top of the valve assembly.
            For a push pull backwash valve shaft leak, this involves undoing the top plate that the shaft goes through either by unscrewing the collar or the two screws on both sides of the top plate, removing the entire piston assembly, using a pin driver or nail with the head cut off to drive the pin, holding the handle on the shaft, out, pulling out the entire shaft, removing the o-ring in the groove in the inside of the top plate, replacing it with the "specific" o-ring designed for your specific valve. Then using the appropriate lube to coat the shaft, o-rings, the inside of the housing, ... (No Vaseline, it eats rubber), reinserting the shaft in the top, and reinserting the pin through the handle and the shaft and through the other side of the handle. This is not easy. Given the amount of time, this takes, and how frustrating getting the pin back in can be, you might want to hire a professional.  
        For a dial backwash valve shaft leak, my suggestion is that you call a professional. Just to pull the two halves of the valve apart, there are "special" positions to put the valve in. Then, although the process is similar, drive out the pin, or, with some older models, Unscrew it, ... finding the right replacement o-ring can be a pain, then there is the idea of compressing the assembly with the spring in place, getting everything back in the correct position, ... I don't "Like" these repairs because of how complex they "can" be. If you are going to do this one, make sure you can get the correct o-ring first, and understand that, if you botch this, it can cost you a couple of hundred more, just for a replacement valve, plus install. Knowing what I do, I would not do this one as a normal homeowner.  
         2.) My Backwash Valve leaks from the Back Wash Valve Outlet
        For a push pull backwash valve, leaking from the backwash hose or outlet: 
        Repeat the shaft removal instructions above, but do not take out the pin. then, replace the damaged, or missing, shaft o-ring. Note: For some valves the upper o-ring and the lower o-ring, while "similar", are not the same size. make sure you get the exact O-rings for your backwash valve, and that you put them in the right places. Then, use an appropriate lube on the shaft, o-rings, inside of the housing, .. and reassemble. 
        For a dial backwash valve, leaking from the backwash hose or outlet: 
            In most cases, then you have to completely remove the old "spider" gasket, completely clean and dry the groove, properly attach the new gasket so that it won't come loose, properly clamp the gasket down so that it will dry fully in place, with no high or low spots, and yet, won't stick to the upper housing, but so that it won't pull loose the first time you back wash, ...  
        Even finding the appropriate gasket can be a pain. If your Backwash valve gasket is damaged, lifting, cut, missing, ... this is another one of those "call a professional" who knows what they are doing, jobs. Due to the complexity, the need for using quick dry epoxy pastes that, the problem with getting the balance between using enough, and not using too much, getting the epoxy in the wrong spots, ... Most people, myself included, will render your valve completely useless, ... after completing their first "Spider Gasket" replacement. These are one of the most difficult repairs to make, and get right, in the industry. While I do this repair, I don't enjoy this one. Too many places for unrecoverable mistakes, or call backs because of leaks.
         3.) My Backwash Valve Leaks from the lid / top of the valve (Not from the shaft, but the top cover where it attaches to the Valve housing.)
           For a push pull valve, Leaking at the Top Cover: take the top off the backwash valve, clean or replace the lid o-ring, lube it as is described above (O-rings and shaft as well), and reassemble. Chances are that if this doesn't solve your problem, you have a crack in the housing itself. (See below) 
            For a dial valve, Leaking at the Top Cover:  Again, disassembly and reassembly can be an issue, as can finding the right o-ring to replace it with. That said, this is easier than the other repairs on a dial valve. "If" you can get the gasket, mark the upper and lower halves with a permanent marker to show alignment before moving the valve handle into the "service" or "disassemble valve" position. Which, if it isn't clear to you, means that I see a professional coming by your house in the near future.
         4.) My Backwash Valve Leaks from the housing Itself
For a push pull Valve, or, For a dial Valve, : Replace the Valve. and  yes, my suggestion is that you hire a professional, and install the new valve with unions. (Click Here)