Loosening a nut on a plumbing fixture can be as simple as using a wrench to release it, or it can be difficult if the nut is lodged in place. A nut can become stuck if it has been overtightened in the past or if calcium, rust, or lime deposits have built up around the nut and have caused it to stick in place. Whatever the case, a little elbow grease and the right tools will usually prove effective.
Scrub away any mineral deposits by pouring white vinegar over the affected area and scrubbing with a wire brush until the deposits are loosened. Rinse the area and allow to dry.
Use a wrench to loosen the nut. Turn counter-clockwise to see if the nut will come free easily. If not, turn the wrench in the opposite direction to tighten. Although this seems paradoxical, if you are able to move the nut at all, even in the opposite direction, the nut is more likely to loosen when turned in the correct, counter-clockwise, direction.
Hold a centre punch onto the nut and tap it with a hammer, taking care not to hit the surrounding plumbing. Try to loosen with the wrench.
Hold a hair dryer or other heat source, such as a propane tank, near the nut. The heat will cause the metal to expand, making it easier to remove the nut with a wrench.
Squeeze a stream of lubricating oil onto the nut. Allow to set for a few hours. Do this every four hours over the course of a day. Loosen with the wrench.
If the above methods fail, the nut may need to be cut away using a hacksaw. Consult a professional plumber to perform this service if you are not familiar with the process.