Lennox g50-36-90 furnace with a hvi 2100

[Tbaron]

I have attached a couple pictures to help you understand what i have. My furnace does not always turn on like it should...the tempature gets way past what it should be. Sometimes when the furnace does start it kicks in and out 4 times then shut down without heating the home. Also the one picture that shows the thermostats the top one is for the hvi and it is no longer working does this affect my furance as well

Help please with suggestions as it is very cold here