I have a Trane combined heat and air unit. The heat is working intermittently. When it quits working the word "Heat" flashes on the thermostat. The weather has been above freezing for the past four days. Last night it did get down to 30 degrees but a week or so ago it stayed below freezing for several days and I had no issues.

Its hard to help with out knowing what you have. Trane-- gas furnace or heat pump? Some thermostats flash when its in timedelay and some flash to show when they are running in that mode.