Bridgeport 412 with Heidenhain 2500 will not Reference Home

Hi All ,

I was using the machine yesterday and everything was fine but when i started it up this morning the Z axis will not home. The head moves up and then feeds down slowly with out Homing.
I replaced the Euchner Z limit switch and the same thing happens.I checked all the breakers and relay switches , still the same thing.
It seems like the Heidenhain control is not getting a signal back saying it's home.

Any help is greatly appreciated !!
Thank You