I am trying to install a new Noma Thermostat, but I threw the old one away so I can't copy on the existing wiring. In fact, I have a red, a yellow, a green (that did not seemed to be used) and a black wire, but no white one. I had connected the black wire in the spot for the white wire but it does not work ? Il also tried to change the HG jumper for HE since I have an electrical furnace. It does not work either. What can I do else ?

Without knowing more about the tstat you threw out or about your furnace we have no clue if you bought the correct Noma tstat. Open your furnace and look at the wire colors coming off the control board, do they match what's coming out of the wall where you mount the stat?

The problem is that I can't reach the box. But what I see following the wires, I would say yes.

I have installed 2 years ago a Noma Tstat on the first floor of my house, copying the existing wiring(black and white), and everything works. The problem happened when I threw away the second floor Tsat this summer.I did not think that the furnace would not heat the second floor because of that. And now, trying to correct the situation by installing a new Noma tstat, I have the problem I described previously. Thanks for helping.