Record the pattern
A furnace that repeatedly starts and stops before the house becomes comfortable needs attention. Note approximately how long it runs, whether the thermostat reaches its setting and when you first noticed the pattern. An occasional normal cycle is different from a recurring failure to maintain temperature. A written description is more useful than guessing which component needs replacement.
Review recent changes
Tell the technician about a new thermostat, filter, blocked room vents or building work. Make sure normal supply and return openings are unobstructed. If the filter is due for owner maintenance, follow the specified replacement procedure and use an appropriate part. Do not remove the filter permanently or close off more registers in an attempt to force air elsewhere.
Do not defeat a protective shutdown
A shutdown may involve equipment protection, so repeatedly resetting it is not a solution. Leave internal diagnosis, electrical testing and combustion checks to a qualified technician. Report any safely visible fault indication. If you see smoke, smell gas or hear a CO alarm, leave and contact emergency services from outside. For other recurring problems, call to discuss an appropriate appointment rather than continuing to experiment with controls.