I replace two X10 wall switches today (only 1 was bad - I misdiagnosed the other case). Now none of the wall switches respond remotely. Before I reverse my effort to track down the culprit (electricity is not my favorite thing to mess with) does anyone have a theory of what might have happened.
One of the two wall switches was new, the other used.
Did you bench check the units before installing them, IOW, are your sure the used switch really works? What make and model number switches are we talking about?
I'd take the "yanked" switches, hook them up to a line cord and a lamp and make sure they are bad. I'd test them in a part of the house away from where they are currently installed and with a plain incandescent bulb. I've replaced a good gear thinking I had correctly ID'ed the problem when it was actually something else.
None of the new switches or no switches at all?
Bad switch, unrelated signal sucker coming on line somewhere else in the house recently, noisy CFL's. Are you using Compact Fluorescents in these circuits? If so, the easiest test is to replace the CFL with a regular incandescent. If the plain bulb works, you're experience either noise, signal sucking or both from the CFL bulbs. That's the most common cause of remote control failure these days in X-10 lamp circuits.
The symptoms of a noisy bulb are often that you can turn the unit ON remotely, but once ON, it generates so much line noise that it can't be turned OFF remotely, only locally.