So here’s the odd thing: I called SmartHome today (since I bought the filters from them) and described the situation. When I got to the part where I said “so I’ve installed the filters and now the towel…” the guy jumped in and said “let me guess: the towel heater is going off and on at the correct times but you’re still getting sporadic light flickers.

Well, color me dumbfounded. I said “um. yeah. That’s exactly what’s happening — how did you know?”

He said “Let me describe your switches; see if I’m right: they’re X-10 brand switches and have a rocker top with a small toggle tab underneath the toggle.”

At this point I was positively boggling — how did he know?! I didn’t even buy the switches from SmartHome, so it wasn’t like he was looking at an order history.

Well, it turns out that those switchs are known for doing this. In these switches, the power used to drive the X-10 circuitry goes through the filament itself. What happens is when a large, short load is put on the line (like a fridge coming on, or the UPS doign the thing it does to recharge itself), the filament dims, and it’s as if there were a momentary brownout. The switch gets confused, loses its state, and then, when the power comes back up to “full speed”, the switch interprets that as an “on”. Equals light on in middle of night for no good reason.

He said the solution is to move up to better switches that use the neutral for the X-10 circuitry (Switchlinc) and that are not so sensitive. Sigh. And they’re $44 each. I do believe him, though, as he *nailed* my problem exactly. He also suggested switching house codes on those switches to see what happens, so I’ve done that and will report back.