Advice needed plumbing tool choices

Anybody use this?

Need to replace 17 series shower valve. Bonnet nut is stuck

Got a stuck bonnet nut. Tried vinegar. Now ledt with brute force, cutting it off, or trying m18 fuel heat gun to loosen calcium, but the Delta Faucet rep said I’d melt the cartridge plastic. Terry love plumbing website says you have to grab the rough in with a wrench but my rough in isn’t exposed enough to grab.

Are there “slim” wrenches to grab a barely exposed rough in?

Is the Amazon tool above worth it? I tried voice grips and got nowhere. The rough in was starting to twist and deform.

Do you believe the m18 heat gun is a bad idea?
Cut depth is an unknown so I am afraid to cut and damage the rough in threads.

Thanks in advance!

Some videos that may be helpful (not sure if these are the same type valve as you have):

I have not used the tool you referenced or worked on a Delta shower valve, but old plumbing nuts always seem to be stuck and over the years I have tried all of the removal methods you mention. Brute force usually ends up with the worst results in my experience.

In any case I would recommend having parts on hand, a supply house open, and lots of time and patience!

Thank you, I will check these out. It’s a known problem yet no seemingly good solution or I imagine the engineers would have invented a problem not subject to these issues.

Can you easily get to the edges of the bonnet nut? or is it recessed in the hole

Did you try putting a rubber strap wrench on it?

Failing that I would heat it and it will take quite a bit to get to the plastic melting temp so I wouldn’t worry as you aren’t using an open flame torch for heat. I would also try some spray penetrant oil like PB blaster. Regardless you’re throwing away the cartridge so no worries.

Finally if you can easily put hand on it - if all else fails cut it. USe a hand saw though and you’ll know when you’re though it.

Bonnet nut is exposed with about 1/8 of the rough in, so I cant stabilize it. I tried to torque it and the whole rough in deformed and made a creaking sound so I stopped and I called delta and posted here. I may still try the heating, but I am afraid because I cant stabilize the rough in since its behind nice tile. Thanks for your assistance!

AH SO. can you put your trim right up again - and mark the tile. Then gently widen the opening till you get near your marks. So as to have a bigger hole to get some pliers in there to stabilize the pipes?

That might be worth doing.