The furnace stopped before the pasta timer reached two minutes. Then it started again. I was standing in the kitchen with a colander, trying to decide whether I had always heard it do that.
My first phone note said 'furnace weird'. That seemed unlikely to help anyone. I added the time, the thermostat's room temperature and the fact that the house was getting cooler. I could hear the fan after the heating sound stopped, which was another detail I would otherwise have forgotten.
Short runs are a symptom
Source: Carrier: furnace short cycling
Frequent starts and stops can have several causes. Carrier identifies restricted airflow, thermostat problems and equipment sizing among them. A dirty filter can restrict airflow enough to trigger a protective shutdown. That does not make every short cycle a filter problem.
I checked the owner-accessible filter according to our manual, with the system off. It needed replacing. I used the specified size and type, then walked through the rooms looking for blocked supply and return grilles. The new shoe cabinet had claimed one of them.
I left the furnace's internal panels alone. I also stopped switching the power off and on in the hope of getting a longer run. Repeated resets would not tell me why it was stopping.
What went into the service call
I gave the technician the model, the visible fault indication, whether the fan kept running, and whether the room reached its setting. I described the filter change as something I had done, not a diagnosis. When the short runs continued, I arranged service rather than another experiment.
There is no useful universal cycle length to chase with a kitchen timer. What mattered was the repeated change in behaviour and the falling room temperature. Dinner was overcooked, but my account of the furnace was finally specific.
