The noise interrupted the radio. It was a sharp bang from downstairs, just as the heating started. I went as far as the basement doorway, then stopped myself from doing the thing I usually do with an odd appliance noise: making it happen again.
I could describe the sequence already. There had been a call for heat, a pause and then the bang. I did not need a better recording badly enough to repeat it.
A sound is not a diagnosis
Source: Carrier: furnace troubleshooting
Carrier identifies loud ignition as a symptom requiring professional attention. Ductwork can also make noises as pressure and temperature change, but a homeowner cannot safely identify the cause of a sharp startup bang from a description alone.
I stopped using the furnace through the normal control, because it was safe to reach, and called for service. I left the cabinet closed. Burner adjustment, ignition work and combustion checks were not jobs for my phone's search results.
If there is gas odour, smoke, fire or a CO alarm, leave immediately and call emergency services from outside. Do not stay to gather an equipment history.
What I could tell the technician
I gave the model from our paperwork and said exactly when the noise occurred. I mentioned that it was new and that I had stopped the system. I did not call it a cracked heat exchanger or a dirty burner. Those were possibilities for someone qualified to investigate, not labels I could assign from upstairs.
While waiting, we used another room and made a safe plan for staying warm if the repair took longer. I turned the radio back on. The useful thing I had done was stop, describe and arrange help, not prove that the furnace could make the noise twice.
