Copper sweating

I've had quite a bit of novice experience now with copper and can make perfect joints with almost every fitting. However, the one fitting I can't make work is the male threaded fitting such as is threaded into a rough valve for a tub-shower. The sweated half of the threaded fitting NEVER seems to want to accept solder. I've cleaned the fittings perfectly but my solder always seems to want to bead up and run right off the fitting. There is absolutely no capillary action. Why do I have trouble with just these fittings and how do I fix it? Thanks so much!!

Please clarify what you mean by "Rough Valve." for your threaded fitting.

Many times, it is perfectly safe, effective, and reasonable to use CPVC to complete your plumbing system behind the shower walls.

Yes, you can sweat (solder) these joints effectively, but upon evaluation of your particular situation, ask yourself: Can the water be turned off completely and the water be drained sufficiently to make a soldered connection?

Do you have room to apply a nice flame to the entire solder area?

compression fittings are a definite must-try. In tight situations you need not worry about much of anything.

fittings

Two things I would never suggest would be to use compression fittings inside a wall, or transition to CPVC at the valve. His soldering procedure is wrong and he may not be using sufficient heat to overcome the mass of the shower valve, but the copper should be soldered into the fitting before attaching it to the valve if he wishes to avoid damaging the internal parts.

The rough valve is exactly that....it's the valve that the thermo element, etc. plug into after your finished wall is up and trim is cut back. It's a hans grohe valve. Plus, it's all brass, there's nothing to damage inside it. I suspect my problem is heat (not enough) but I just want to make sure. There are 4 ports.....cold in, hot in, tub out, shower out. The valves that thread into the 4 ports are all sweat joints on the opposite side. Those are the joints I have problems with and I suspect, as I said, that more heat is the key to success. Thanks.

When I'm installing male adapters to a shower "body", I sweat the fittings onto copper pipe, cool them and use pipe thread sealant (dope) and thread them in.

I like to have a few inches of copper exposed before the next joint.

I don't really like to use Teflon tape which can leak if it's over heated.

If I'm soldering directly to a brass body, I pull the cartridge and set it aside until I'm done.

When I'm soldering, I clean the pipe and apply flux to the pipe. Even heat on both sides is key.