Has anyone used a LED light in an Omega C700 Condenser Enlarger? I've tried it once and it worked well but when I tried to use it again the light started flashing. I'm using an 11w warm white LED light. I'm also using a transformer as my enlarger requires 120v and I live in a country that uses 220v. Could this be a reason for the light not working? Or is my enlarger just getting old?
It's likely that your problem is due to the interaction with the LED and the power transformer. A more expensive (probably much more expensive) transformer will likely smooth this out. The enlarger itself is relatively simple and I don't see anything about it where age would cause a problem like this. So, this isn't really a photographic problem, more a general electrical lighting one.
From a photographic perspective, be aware that all white LED bulbs are actually fluorescent light sources, and do not produce a complete spectrum like an incandescent bulb would. "High CRI" bulbs are better, but not necessarily sufficient. This will be less of a problem with black and white, but may give you visibly poor results in color.