breaking loose steam traps

I was not able

to get my caps off. I don't think they were ever serviced (88 years). When I removed them from the radiator and pipe, I put them in a vise. Using a cheater bar and pipe wrench, I finally got the caps off, but egged the fitting.



If they are that bad replace the whole shooting match.

Impact

Impact is your best option. If you don't have an impact wrench or air hammer you can do it the old-fashioned way with a hammer and cold chisel. If the fittings are malleable you can notch them and then drive them at a tangent from every possible angle to try to unscrew them. If they're hard cast you can usually break them with a big enough hammer.



Heat is only helpful if you can heat the fitting faster than the pipe, or heat both and rapidly cool the pipe so it contracts and fractures the hardened pipe joint compound that's locking the threads. You can sometimes loosen them up just by persistently beating the fittings with a hammer, but if you only hit it in one or two places you can deform it, making it harder to turn even if the threads break loose

Try to tighten them first

After heating and waxing tighten them just a bit then loosen them.