This didn't even occur to me at first but it's a valid point. As old as the car is, a wire being bad is a distinct possibility.i agree with temp sensor being bad or the wires could of snapped, its happened to me in both my integras, the wires the clip goes just snapped
I definately agree a possible airlock but usually not a problem if radiator sits higher than cooling jacketscheck your coolant level and make sure there's no bubbles in the system