I have forced hot water and had a second zone added when I built an addition about 25 years ago. I just turned the heat on but the heat isn't getting to the addition. I've checked the circulating pump and it is on but I noticed that the pipe on one side of the taco 219 swetcheck is hot while its just warm on the other. Is the swetcheck the problem?

I believe you are talking about a Flow Check valve made by Taco. Is this a picture of the item you are talking about.

Mine is an older version with a thumbscrew on top but yes, that's the valve

Probably not the swing check. There should be a valve that controls the water flow to the second zone. Find that to start with then you can track down the control voltage to see what is preventing it from opening to allow water flow.