Observe the pattern
Check whether the thermostat is requesting heat and whether the fan is set to run continuously. Note whether air stays cold through the heating attempt or only briefly at the beginning or end.
Know when to arrange service
If the house is cooling and the furnace never delivers heat, follow the No Heat path. Give the technician the timing, thermostat settings, and any visible fault code.
Take this question into the conversation
“What did you find, what will the proposed work solve, and how will we know it worked?”
This is general educational guidance, not an assessment of your equipment. A qualified contractor must evaluate the actual system.