Stuck brass compression fittings

I wouldn't have thought so, although it wouldn't do any harm. If they're standard brass compression fittings with olives then basically you're not giving them enough grief. Try a bit more force; they'll definitely give at some point.

Heat helps with most tight threads, but use a shield to protect anything that you think might crack. I very much doubt that WD40 (or plusGas) will do anything useful in this case. Try pulling harder!

If you can't undo them with two properly fitting spanners then you have a bit f a problem. Is it rather inaccessible? If the spanners

Alternatively, again depending on accessibility, try tapping one side of the nut with a heavy weight behind the other side - i.e. 'squash' the compression nut with your hammer taps. Do this in different directins (as access allows).

I don't think WD40 will help, proper penetrating oil might help but not a lot I suspect. I find that penetrating oil is only really a help after you've actually managed to move the joint, then it makes it possible/easier to undo.

Yes the basin is in a vanity unit with very little room to apply leverage. I disconnected the drain outlet and propped the basin up on wood blocks to give a bit more room but I can't lift if far because of the length of the tap tails. I got one tail off but the other b****r won't budge.

If all else fails, cut the tails, remove the basin, remove the remains of the tails and get a new pair.

Cut the pipe?

Agreed, but one other thought.

If the problem is getting enough "grip", have you tried using mole wrenches on them? These days they come in a great variety of sizes and grip types. For brass on brass, I'd expect this to work provided you have room to get a pair of wrenches on them. You need to do up the adjustment screw so that you can only just get them to close, at that point the teeth will be digging into the brass. I have been known to use another mole wrench to get the first one closed.

Another thing you could consider is using a "dremel" to split one of the offending nuts. Use the fibre-reinforced "grinding" disks which will tolerate a bit of side force. Forget using "stone" or "burr" type bits.

Once you have done that, it's goodnight Vienna on getting a new one on. Because of the olive

you can get an olive splitter for that.

The new tap has its own tails. I'll try heat before doing anything too drastic.

and pullers:

Some good ideas. I have 2 Mole wrenches. I also have a 'dremel like' tool (Chinese Knock-off?) but I don't thing it's up to cutting brass.

It's very short already, being used to connect the service isolator to the tap tail and I can't unscrew the isolator's nut either. I'm beginning to think the original installer must have used some sort of sealing compound on the threads. I'll try heat.

Don't forget your safety googles.

You'll be pretty close to the work.

Paul

Possibly "brake spanners" would get a better grip? Like a ring wrench with a gap...

Make sure the pipe is dry if you want to get it hotter than boiling water.

Thomas Prufer

you still have a pipe hat has been 'waisted' that will be hard to get a seal on again.

Use a junior hacksaw at 45 deg. to cut the olive until it's almost through (the angle avoids cutting the pipe), insert screwdriver and twist - olive is gone. Use new olive in same place as the old one.

Like:

But if it's been done up *that* tightly - as appears from the OP - then the pipe may well have been deformed beyond correction by the old olive anyway.