I have had that happen to my ceramic heat emitters on my Beardie enclosure. It usually happens after about 6 months, so I kinda just expect it now. One thing you can try is a Radiant Heat Panel. They are similar to CHE's but are guaranteed to last 10 - 30 years. It raises the ambient temp just like bulbs and CHE's. They are more expensive that CHE's ($80 vs $20) but they last so long that it pays for itself.