Moderator Post (s) for this thread: >knocking pipesbyBillhart on 09/18/2007
The nipple is the short piece of pipe between your water heater and the rest of your pipes. Look at the top of the water heater. The short piece of pipe that connects directly with the water heater is the nipple (male threads at both ends); the other end of the nipple connects to your house pipes. I'm not sure how you would tell if the nipples are the "energy efficient" type or the standard "non energy efficient" type without taking them off and shaking them to see if they rattle or not.
Is the noise coming from the top area of the water heater? I had a similar problem. The ball in those "energy efficient" nipple would chatter/rattle loudly and continously on any heavy hot/warm water usage. Plumber said that's normal but the noise was loud and very annoying. So I had the nipples replaced with regular pipe nipples. Don't know how much more I'm paying in gas for those "non energy efficient" ones, but I now have peace and quiet.