Plumbing Problem

My home was built with Qwest PB pipe. When it failed, the company paid to have my house replumbed in copper. Since then, whenever we turn on the hot water spigot, particularly in the bathrooms, there is a small burst of air. There are no plumbing leaks. Someone told me that there is a cannister of some sort in the line that elinates the problem, and that the cannister is bad, but I cannot remember what it is. Can someone explain the source of the problem?
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mcp6453 wrote:

May have been thinking of a thermal expansion tank: http://www.zurn.com/pages/catalog.asp?ProductGroupID &OperationID Look at Model HXT.
Mineral conditions inside the water heater may be producing small amounts of gas (not air) which rises to the top of the tank. I'm not sure that an exp tank will solve that.
If your water source is a well, I would suspect gases produced from interaction with the magnesium anode rod.
Offhand I can't see a connection to the piping replacement.
Jim
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Speedy Jim wrote:

It may not be related. How do I troubleshoot? Replace the expansion tank? The water heater is about two years old. We're on city water, not a well.
Thanks.
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mcp6453 wrote:

It already has an expansion tank? I would put a pressure gauge on the tank (at the drain cock) and watch the pressure as the heater fires (with no water being used). If pressure goes up sharply, the exp tank may be bad or need air. I'm grasping at straws, not being there to see it.
Ask neighbors if they have any similar problems.
Jim
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