When your heat stops working on a cold Upstate SC morning, the first instinct is to call for service immediately. That's sometimes the right call — but a few quick checks can save you a service call if the problem is something simple.
Start With the Thermostat
Set the thermostat to "Heat" and raise the set temperature at least 5 degrees above the current room temperature. Make sure the fan is set to "Auto," not "On." If the system doesn't respond within a few minutes, check the display — a blank screen may indicate a dead battery or a tripped breaker.
Check the Air Filter
A severely clogged filter restricts airflow and can cause a gas furnace to overheat and shut off on its high-limit safety switch. If your furnace runs briefly then shuts off, a dirty filter is a common cause. Replace the filter and try again.
Check the Circuit Breaker
Heating systems — both furnaces and heat pumps — have dedicated circuit breakers. Check your electrical panel for any tripped breakers. Reset once. If it trips again, don't keep resetting it — there's an electrical issue that needs professional diagnosis.
Gas Furnace: Pilot Light or Igniter
Older gas furnaces use a standing pilot light. If it's out, the furnace won't fire. Check your furnace manual for relighting instructions — it's usually a straightforward process.
Newer furnaces use an electronic igniter (hot surface igniter or spark igniter). If the igniter fails, the furnace won't light. You may hear the furnace try to start — a clicking sound — but no heat follows. This requires a technician to diagnose and replace.
Heat Pump: Defrost Mode
Heat pumps occasionally enter a defrost cycle in cold weather, during which they temporarily blow cool air. This is normal and lasts 5–15 minutes. If your heat pump is blowing cool air continuously for more than 20 minutes, that's a different issue — see our article on heat pumps blowing cold air in heat mode.
Gas Supply Issues
If you have a gas furnace and smell gas, leave the house immediately and call your gas utility from outside. Do not operate any switches or appliances. If you don't smell gas but the furnace still won't fire, check that the gas shutoff valve near the furnace is in the open position (handle parallel to the pipe).
When to Call a Technician
If you've checked the thermostat, filter, and breaker and the system still isn't heating, it's time to call. Common professional repairs include failed igniters, faulty flame sensors, failed draft inducer motors, and heat pump refrigerant issues — all of which require a licensed technician.
Frequently Asked Questions
My furnace turns on but shuts off after a few minutes. What's wrong?
This is often caused by a dirty air filter triggering the high-limit switch, a faulty flame sensor, or a cracked heat exchanger. Replace the filter first. If the problem continues, call a technician.
Is it safe to run a space heater while I wait for HVAC repair?
Yes, with precautions. Keep space heaters away from flammable materials, never leave them unattended, and plug them directly into a wall outlet (not an extension cord). Don't use them in bathrooms or near water.
How quickly can Garris Air respond to a no-heat call?
We prioritize no-heat calls, especially in cold weather. Call us at (864) 237-5363 and we'll get a technician to you as quickly as possible.