I have a gas furnace and ac all in one Rheem unit in my attic. It is just a few years old. They did not change out the thermostat or wiring. Every year since installation the heat would work during mild cold temperatures. But as soon as we have a cold temps in the 30s the heat will not come on and it is cold in the house... about 60. So every year the people that installed the new unit would come out and say it was the batteries or something and later in the day, once it warmed up, the heat would come on. After that it seems like the heat works fine for most of the cold season.

So this year we installed a new Honeywell rth230b and both heat and ac have functioned fine since then. I have a R W Y G wires with Rh and Rc jumpered.

This morning was the first morning in the 30s and now the heat won't come on.

I tried to follow some instructions on one post to jumper the red and white at the thermostat but nothing happened. The next instructions were to jumper the red and white at the unit, but I am not sure exactly what to do.

When I look at the wiring strip at the unit I see the 4 wires coming from the thermostat, R W Y G, and a red and white wire coming off the terminal block and going out and down towards my basement. So is it the R and W from the terminal block that are NOT coming from the thermostat that I jumper at the unit or the R and W coming from the thermostat?

There is a safety switch that the door removal activates. When I push that in I got two green lights, but the amber light for the flame doesn't come on.

Any ideas on what the issue might be and how to fix it. The post I am trying to follow is the #7 under General questions here.

https://www.askmehelpdesk.com/heating-air-conditioning/heating-cooling-maintenance-repair-troubleshooting-faq-northerheat-58313.html

OK what happens when you see the amber light. Does the vent motor run? Is the blower running? Does the ignitor glow? And does the unit vent with metal or plastic pipe?