We have a PowersControl shower valve body that had a model 420 cartridge et al and the company has made a retrofit to upgrade the entire unit to one that uses a wax element to control temperature fluctuations, I think. Powers is now a subsidiary of Watts Water Technologies
I have never done any plumbing in my life, except for snaking out drains and I once replaced a copper pipe trap with a PVC one. So my knowledge is limited, and could be dangerous.
The Lucite handle we had for the shower, that came with the shower, wore out from the inside and it wasn't grabbing anymore, and there are no old handles that fit those 30 year old Powers stems. So for the time being, I took a handle from another shower that hade the same valve controls. However, now the bathroom for the guest room and my office, which I might start using because it takes my fiancé too long to get dressed and put on her makeup.
On that shower we hardly ever used and now without a handle, we were getting a little jack hammering for a second on turn on and turn off. The plumber said that happens with showers not used. He said, everything inside dries up. The plumber told me we needed a new cartridge and gave me a price of $295 plus installation, if they had it in stock and of course, if it wasn't made anymore, a new shower valve body would be needed and that is a great deal more. So, I was looking at least $600 if everything was available and much more if not. Believe me, the plumber told me they don't make it anymore, I wouldn't know the difference.
I decided that I just needed a handle and I was going to live with the jack hammering, as it isn't a shower we used every day. Actually I now see how that would have been a very bad idea from reading other postings above mine. I also noted that the hammering happens more when there is a pressure assisted toilet and we have one of those too. So that and the fact that that shower was never used, caused the jack hammering.
Back to the Powers valve mechanism, there are no handles for that stem anymore so I had to put in their retrofit kit. I wrote to the Powers people and told them about my situation. They sent me information on the install and they gave me someone who would stay on the line and talk me through it. Totally as a surprise to me, they also offered to send me the retrofit kit and handle, at no charge, a $230 value. I only expected they'd find a handle that fit the old stem.
I felt like I was in the Twilight Zone, where an American company was that nice and that responsive. With this Power's employee John's help, I opened the bonnet and took out everything I could. There was one white plastic ring thing with 4 square legs and it was actually much more substantial than a ring. That had to come out but after 30 years it wouldn't. I tried pulling it but my pliers didn't have enough treads all the way to the top to grab the little legs. Then John suggested trying to pry it out with a screwdriver. It just would not go. The last resort was to chisel it out. I did and that worked great.
So, the shower valve was empty, except for hot water seat in the back. It took a 7/8 hex socket to unscrew it. I had one but mine was beveled, as most of them are. The hex part of the seat was very shallow, maybe a 1/16th of an inch and maybe it got only half way up the bevel. Luckily John told me not to go ahead because if I stripped the corners, I'd have a real big job for a plumber.
So, I went to Home Depot. That store is not stocked like it used to be. I actually went to two them. They had only and 12 point but that was also beveled. However, one of the guys in the tool department told me that I can grind it down but that would void the warranty of the hex socked. Like I care about the warranty and a $4 hex socket. That was my second Home Depot and then I went to a good hardware store and an auto supply store and neither had anything.
I went home and decided to put the bonnet back and ask John to send me the correct socket, which he offered to do. How nice can you be? However, putting on the bonnet didn't stop the water going into the bath or shower and I think a piece of plastic might have gotten lodged in the drain so the water was not even draining. I then realized I have to try to grind that 7/8 hex socket down. I have only used the wheel twice to cleanup screwdrivers that now look more like picks, after I finished with them. I did the best I could. It wasn't perfectly flat but it was enough to grab the seat and unscrew it.
So know with the very good instructions and what John told me before I went out to look for the unbeveled socket, I was able to get the retrofit in and working great and it is so smooth and so easy to turn.
So, Watts Water Technologies is one hell of an American Company and I was ecstatic dealing with them. I do not work for the company or have any relatives that do. They took a terrible situation and fixed it!
Alan