News & Media

Furnace blowing cold air: the likely causes, most common first

| Heating Articles and Advice

A furnace blowing cold air is most often caused by the thermostat fan being set to “On” instead of “Auto”, a clogged air filter that makes the furnace overheat and shut off its burners, or a dirty flame sensor that shuts the burners off seconds after they light. Fix the fan setting and the filter yourself. If the air is still cold, the cause is usually ignition, the flame sensor or a safety control, and that needs a licensed technician.

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Furnace not turning on: what to check, and when to call

| Heating Articles and Advice

If your furnace is not turning on, check that the thermostat is set to “Heat” above room temperature, the furnace power switch is on, the breaker has not tripped, the filter is clean and the furnace door is fully closed. If all five check out and there is still no heat, the cause is usually inside the furnace (the ignitor, flame sensor, pressure switch or control board), and that is a job for a licensed technician.

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