I have a transformer that is 120/24 one side of the transformer going to the board is reading 24 volts like is supossed to the other side going to the control board is only reading 8 volts I don't know what the problem is

Whether the transformer is on load or what?
How much is the distance between the board and transformer? What is the capacity / rating of the transformer? What is the size of cable used between the transformer and the board?
You may find your answer / remedy out of above questions / queries. Thank U.

Agreed, check the wires. You could have a short to ground in your low voltage system.