What interrupter are you using? I assume you are using an interrupter and not the QRB1114 reflective device.
the first thing I would do is get a digital camera and look at the LED. It is a little hard with an interrupter but it's possible. The LED should show up in the LCD display if it's lit. If you can't see it then the problem is with the LED (backwards, low current or burned out).
If you can see it then you need to determine if the ptrans is working properly. First thing, get a piece of black electrical tape and put it on the ptrans windows. That should cause the PT to stop conducting and you should measure the full voltage across the PT. When you remove the tape, the voltage should drop pretty low - the GP1S53V would have around .4V across it - but not to 0. See the datasheet for your interrupter.
That circuit is pretty simple, not much can go wrong.