Electronic – Potentially unusual LED failure

One of the LEDs in a plug equipped with over-voltage protection does not light up when the device is plugged into the 230 V mains. It has worked well for a while since the product was purchased. An inductive load was used with the plug.

After I took it out of its board, I checked it with a multimeter on the "diode testing" mode and found out that it conducts in reverse, with a voltage drop of 1 V. Despite the fact that it does not turn on, my multimeter shows there is a forward voltage drop of around 1.8 V, which seems to be a normal value for a healthy LED.

I was expecting open-circuit and short-circuit failures, but none of these seems to be my case. Since it conducts in reverse, it must have experienced reverse breakdown at some point, too.

Here's a schematic which can give you and idea about the circuit in which my component was:

^{simulate this circuit – Schematic created using CircuitLab}

The LED and its resistor are in parallel with two varistors, 230 V supply and the load which connects to the plug.

Here's a photo of the LED:

What could have caused something like this?

Has anyone seen something like the aforementioned LED has failed? Maybe something very similar?

EDIT: The green LED did turn on with the help of a few batteries, but all the other things still apply; still showing reverse voltage drop of 1 V without turning on (both for multimeter and batteries methods). Still doesn't turn on when connected to the multimeter.

NOTE: The green LED was replaced by a new one in the device it was part of and that new LED lights up without problems.