Powerline (eg. X10, Insteon, UPB) automation signals travel along the household power wiring.  There are two main issues that can affect performance.  One is that your house electrical system is split in to 2 phases at the breaker panel.  The other issue can be "noisy" electronics in the house.

First let's talk about "phase issues".  Since all houses split the 220V incoming supply in to two separate 110V phases, it's recommended that ALL installations have some sort of a coupler or repeater installed.  In some small installations where only one or two switches are used and especially if they're on the same phase, this isn't an issue.  But when multiple products are installed it's really a requirement in order to create a solid foundation for X-10 or Insteon powerline communications.  Some require installation at the breaker panel which means they should be installed by an electrician.  Others are plug-in style devices.

We have several X-10 couplers, please see part #'s:  XPCP, XPCR, HCA02-10E, 4816A2, 4826A
Insteon couplers include: 2442 (2442P), 2443 (2443P), 2406H.
Part# 2406H is an interesting choice because it's inexpensive and works for both X-10 and also Insteon networks.

Insteon networks use the 2442 or newer 2443 SignaLincs to couple the phases in your house by simply pluggin in two or more in to the right outlets in your home.  There is also a part# 2406H which is hardwared and is a coupler (not a booster) for both X-10 and Insteon.

As a quick test to see if "phases issues" are your problem, try turning on a 220V electric stove or clothes dryer and see if there is any improvement to the troubled switches.  If so a simple coupler might do the trick.  If not, you may have other noise issues compounding your problems, or you may need a coupler/repeater which not only joins the two phases but also boosts the signals across both sides.  These are common for homes over 2500 square feet.

The other issue that can impact any powerline technology is noise or attenuation caused by lights & appliances in the homel. Some known problem devices are computer UPS's, power bars, computer power supplies, motors (furnace motors, pool pumps) , CF (compact fluorescent) bulbs, fluorescent light ballasts, TV's, stereos, etc.

The key to diagnosing noise/attenuation problems is to do a little detective work and to be patient. There are two strategies. One method is to turn off all the non-essential breakers right at the breaker panel. This is a fast way to disconnect most of your household electronics. Of course you can't turn off the breaker to the devices you're using as senders or receivers. The other method is to UNPLUG all your household noisemakers including power bar & UPS if you have one, TV's, stereos, etc. It's not good enough to turn them off, they MUST BE COMPLETELY UNPLUGGED. Then see if your powerline devices are working better. If so, gradually turn breakers back on or plug electronics back in and keep testing to see when the problems start to re-occur. Once you find the culprit, you can use a powerline FILTER to fix the problem.Â

For plug-in devices, see part#'s:Â Â XPPF, 1626-10
For hadwired filters: XPNR, XPF, 6289
The XPF is an interesting one because it couples the powerline (see above) at the breaker box and also filters X10 noise from entering or leaving the house at the same time. It needs to be installed by an electrician.

By ensuring proper phase coupling and possibly using filters, it's possible to create a strong, reliable network over the power wiring in your house.