Removing a threaded cartridge

This message board looks good. My first post/problem:

Preparing a Georgetown series Price Pfister tub faucet. The manual says to remove cartridges before sweating. These cartridges are threaded. I have tried pretty damn hard to loosen them. Anybody have tips on getting them out? The cartridge and body are brass. Should I warm them a bit?

thanks in advance,

Pete

Make sure the taps are in the full open position before you try to unscrew them. If you have to place the unit in a vice to hold it, you may have an easier chance to get them loose