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I have a home built in the mid-70's and we are wanting to do some remodeling in the bathrooms. Since I can't turn off those old valves under the sinks, I thought this would be a great time to replace them with new quarter-turn valves.

The problem is, I can't seem to get the old compression fitting off to remove the valve, the nut is frozen to the valve body. One of them has a whole bunch of white corrosion around the threads and I haven't even tried that one yet. They are a brass nuts on brass valve bodies, not chromed, and I think that has facilitated part of the sticking.

I am looking for help in how to un-stick/freeze this valves so I can replace them. I am wary of pure brute force as I don't want to make matters worse, unless that is the only way of removing them. Cutting them off will not work since there will not be enough copper pipe extending out to put the new ones on.

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Start with some penetrating oil and time. Then proceed to mild heat from outside. You want to expand the nut, but not the inner parts. If you have room, a plumber's torch (judicially applied) or a basic flame from other sources. Be sure to steer clear of vinyl parts that could be damaged.

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  • Penetrating oil, like WD-40? Or something different. I have plenty of time, but are we typically talking minutes, hours, a day? Thx
    – Jim
    Jan 8, 2017 at 0:56
  • That's one option, but there are products more specifically developed to penetrate. Liquid Wrench, for example. Start with WD if it's on hand. Half an hour or overnight.
    – isherwood
    Jan 8, 2017 at 0:57
  • OK, I will check out Liquid Wrench. I have had problems with brass-on-brass fittings freezing up before and I don't remember WD-40 being very helpful. In that case it was a garden hose sticking to a manifold that I got for my hose bib. After about a year, it was stuck for good (I live in Phoenix and we use our hoses year round...)
    – Jim
    Jan 8, 2017 at 1:00
  • So would you hope to reuse the original ferrule and nut? Or it you could get the original nut loose, would you have enough tubing to cut off the old ferrule and then put on a new nut and ferrule? Can ferrules be cut and pulled off and new ferrules be put on in essentially the same location?
    – Jim Stewart
    Jan 8, 2017 at 1:51
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    Life got in the way of this project, but I found something like Liquid Wrench as neither big box store I went to carries that brand. This was PB B'laster penetrating oil. I put it on, and because I couldn't get back to it right away, it was left on for several days. When I got back to it today, I was able to get it off.
    – Jim
    Jan 15, 2017 at 20:45
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I have found WD-40 to be a lousy penetrating oil. Liquid Wrench, Sea Foam or PB Blaster are much better. Experience has shown me that none of these are particularly effective on aluminum, I am not sure of their effectiveness on brass to brass. But it is worth a try. My usual method with ferrous fittings is to wrap a small strip of rag around the fitting and soak it for several days. Not sure if it works for brass but I've had good luck with household strength ammonia on aluminum parts. It might be worth a try.

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