I am trying to install a smart thermostat and need some help.

I am replacing a Honeywell wireless system (not wifi) and have one question and one issue.

First off I was pulling the wires from the module in the basement and noticed that each color can allow 2 different wires to be put in. I saw that there were 2 wires going into the Y Terminal (see photo). When taking them off to add to the wifi system I combined the 2 together and added a 3rd wire that goes upstairs to the new thermostat. What is the second wire?

I now have everything hooked up and going (1 stage AC and heater only 2 years old). The ac works perfect and comes on without problems the heat is the problem.

When I turn the heat on the exhaust fan comes on like normal. I took the panel off and watched the process by the blower. After the fan comes on the igniter glows bright red for about 5 seconds then goes off with the flames never starting. A few seconds after the igniter goes our the blower comes on and it started blowing cold air in the house. Does anyone know what is going on? Please help!

I am using an alarm.com thermostat the have the fossil model selected instead of the electric.

I am using the ADC-S3000 thermostat, lennox furnace (95%), everything is 2 ton.

I ran 5 new wires because I had the AC installed a few months ago and they put in the wireless model.

I have a C wire, R wire that is put into the RH terminal (per manual), W wire, 2 Y wires (one ran to the thermostat) and one G wire. I used the photo above to go directly from model to model.

Both ac and furnace have water pumps as well.