XPXPF
If powerline noise from a large appliance is interfering with your X10 signals, install the X10 PRO Wired-In Noise Filter (20A, 3-Wire). This filter allows X10 signals to freely pass through your electrical system with minimal interference by blocking out electrical noise from high-current, 20A devices. The filter also prevents X10 signals from being absorbed by electronics like TVs and computers.
How to Find the Interfering Device
Once at a time, unpower each electronic device near your unreliable X10 receiver. When you see a signal increase (improved operation) upon unpowering an electronic device, then you have detected an offending, noise-generating device.