[johnryan]

When the heat comes on I hear the pipes knock 2 0r 3 times This only happens on the top floor. I have three zones and it only happens when the upstairs zone first turns on the colder it is the more it happens

[mygirlsdad77]

The sound you most likely are hearing is the expansion of the copper heating pipes exanding against the wood they are anchored to or run through as the hot water circulates through the pipes. This is very common, and there really isn't a lot you can do about it without gaining access to the piping and creating space between the wood and pipe