Bathroom fan

[jtimp]

We have had a vent axia Luminair fan with a Humidity Sensor for about 5 years now. Today the fan did not come on. The light on the sensor is lit, and when I removed the cover and tried to clean the vents on sensor (could not fully open up sensor without completly switching everything off) the fan came on for a few seconds (No steam in bathroom by then). Don't want to dive in and start replacing fan, transformer or sensor if I do not need to. Any ideas on how to eliminate the problem