The dryer and stove trick doesn't always work to find 100% need for a phase coupler. Some people have tried it and it didn't help there problem but buying a phase coupler did...
Good point. If turning on the stove/dryer does help, then a coupler most likely will help. However even when it doesn't help a coupler can help.
The signal has to find a path from one phase to the other. Without a coupler this may mean that the X10 signal has to go all the way to the street and back to travel through the transformer there. In the old days before many of our common signal suckers and noise generators this worked more often. So a signal problem can and often needs to be helped in more than one way.
You might want to read the troubleshooting series I wrote:
http://jvde.us/x10_troubleshooting.htm
The ones on Passive Couplers and Filters should help you.
Jeff
Ditto on the above! Jeff is one of our foremost signal experts here. The products that he makes or some of the best for assuring a reliable setup.