Hello my name is XXXXX XXXXX will be my pleasure to assist you. The most likely cause would be the thermostat but if it is not getting to the set temperature on the thermostat it could also be the high limit causing it to trip the high limit which will auto reset. Check the furnace filter and be sure its not dirty and plugged up which would cause the furnace to overheat and trip the high limit.
Its either the high limit or the heat sequencing relay.
Try jumping out the high limit with an unbent paper clip with the power off tke the wires off the high limit and use the unbent paper clip to jump the limit and try it if that doesn't work then it is the heat sequencing relay.
Yes they are both in the furnace the high limit is in the middle section of the furnace and the relay is in the upper portion near the heat bank coils.