My thermostat has a timer (leave/return, etc.) so my furnace will come up to temperature the first time it is asked to, but then will shut off until the next interval. What do you think it is?

Answer

There are hundreds of thermostats on the market so I cannot tell you much beyond reading your manual and double checking your programming. It sounds like something has perhaps been programmed improperly. Unfortunately they all program differently so I wouldn't want to guess.