Temptrol shower valve problems

My Symmons Temptrol (Model B) temperature balanced shower valve is only putting out cold water. Symmons lists this common problem on their website, <http://www.symmons.com/service/product_info.cfm#Q6 and first fix is to remove the handle and tap the spindle a few times with a rubber hammer. That didn't work.
Next, the solution is to remove the spindle assembly. <http://www.symmons.com/ins/temptrol_ins.pdf#page=5 (pdf file)
Here's where I'm having trouble. I can't remove the cap (part T12-A). I've taken a wrench to it and it won't budge despite a lot of torque. I'm afraid to apply any more force on the wrench because the valve is supported by the plumbing inside the wall.
Has anyone had this problem or know what to do? Perhaps heating it a little with a torch would expand the cap enough to unscrew. Thanks!
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Melissa Vascio wrote:

Torch might work. If necessary, put a sheet metal heat shield behind the part to keep heat away from parts that might get damaged. And wear safety glasses!! I'vd had hot particles explode out.
Jim
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Melissa Vascio wrote:

If you can manage it, it would work best to heat the body, around the cap you are trying to remove, so it expands away from the cap.
Remove the diverter valve and the stop spindle assembly (if you can) before you heat things, to minimize the number of elastomer parts you might fry.
Oh, and when you're getting new parts, pick up a new O-ring (N0.24) for the diverter valve. When those get old and start to leak, they drip BEHIND the wall, and you don't know about it until you notice water damage, like on the ceiling of a room below.
You might want to do what I did to all three Temptrol valves in our home. I added little sloping sheet brass chutes under them, stuck on with silicone caulk. These direct any leakage from the diverter valves to the "front" of the wall behind the escutchion, where it can safely drip down the tiles and into the bathtubs.
HTH,
Jeff
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My name is Jeff Wisnia and I approved this message....

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I had a stuck T-12A cap and was able to get it off with WD-40 and an upgrade to a real 14" pipe wrench. My puny monkey wrench was not the right tool for the job. I sprayed the WD40 completely around the cap seam and let it sit for 30 minutes. Save the torch as a last resort - lots of meltables inside the temptrol.
fwiw...Chris
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