The furnace is blowing air continuously
You may need a service call to have a professional check the limit switch and replace it with a new one.
The furnace runs for a short time and quits
If your gas furnace is cycling on and off and won't stay on, and you wonder how long your furnace should run during a typical heating cycle, you may have faulty parts that need replacement. However, the first thing we check is air flow problems. Without proper air flow through the burner, the heat exchanger may get too hot and trip a limit thermostat. We check to ensure the furnace has sufficient intake air and clean air filters before testing for defective parts.
If poor airflow through the burner is not causing the rollout switch to stop furnace operation, it may be that the flame sensor may be unable to detect the flame. The flame rollout switch might be defective.
If your furnace only runs for a few minutes and shuts off - you may have a defective pressure switch which may cause the ignition process to pause. Without proper ignition, the control board will shut off the furnace. Another common furnace problem in Winnipeg winters is the draft inducer motor may be defective. Without proper air flow through the burner, the pressure switch will not close which will cause the furnace ignition sequence to stop.
Check if your thermostat is very close to a heating vent - sometimes this is the cause of your furnace only running for a short time and then shutting off before the house is warm.
