Bulb has blown on one of the lights but the other...

Question

The first time a bulb blew on the cooker hood the other light stayed permanently lit and would not switch off with the switch (the extractor fans continued to work ok with their switches.) The hood was still under warranty so the indesit engineer was called and he replaced the control board. A bulb has blown again and we seem to have the same problem but the warranty has run out. Surely this cannot happen each time a bulb goes - do you know if this is an inherent problem with this type of cooker hood