I have a mueller climatrol furnace in which the gas valve won't open or stay open. We think it is electrical problem. Back in the summer, my air went out and a friend did wiring to bypass so the air would work for time being. At that time, before the bypassing to get air to work, the heat worked. Now he has tried to go back to getting the heat to work and I have neither heat nor air. My concern is the heat. He thinks it is definitely an electrical problem because the gas valve won't stay open. He says juice is getting to the gas valve but just won't open. Any advice would be great. Thank you

Attached is a furnace of the same brand that looks like mine, but not exactly.