Hello I install a new thermostate and now my heater won't star on automatic only on {ON} and if I turn it off and leave it on {ON]still running and swich to auto then turn off I don't know what to do if you can help me letme know,my heat is electric and central heat and ac my ac works fine on auto but my heat won't

Old brand and model of thermostat ?

New brand and model number of thermostat?

Exact model numbers for both thermostats please!

I don't know the old model but the new model its a honeywell ct31 I think the old model it's the same come from manufacture because this is 1990 mobil home

I can't remember the old one but the new one is heneywell ct31 I think the old one comes with my mobil home 1990

Auto what??

Are you talking about the blower that blows air out of the furnace?

How many wires go to the thermostat?

I can't remember the old one but the new one is heneywell ct31 I think the old one comes with my mobil home 1990

Its got 4 wires red,green,yellow,and white

Is this an electric furnace?