I had one of these fitted in my kitchen by a qualified electrician and last week on of the 50w bulbs failed. I bought a replacement from Tesco and fitted it carefully making sure the spring and surround were held correctly which they were as I tugged a little on them and it seemed ok. I switched on and it worked but after about half an hour the whole thing came out and smashed on the floor. The bulb however was whole so I replaced it without the surround and it blew immediately I switched on. What did I do wrong?