If your HVAC system isn’t blowing hot air on a cold day in St. Louis, MO, it’s a sign that the critical heating cycle has been interrupted. While some problems are complex internal failures, many can be fixed with quick, safe troubleshooting steps you can perform immediately.
As your local HVAC professionals, we’ve put together the most common reasons your system is failing to produce heat and what you should do next.
Your Immediate Troubleshooting Checklist
Always perform these basic checks first, as they resolve the majority of “no heat” calls.
1. Check the Thermostat
- Wrong Mode: Ensure your thermostat is set to HEAT (not COOL or OFF).
- Low Setting: Set the temperature at least 5 degrees higher than the current room temperature.
- Dead Batteries: Replace the batteries immediately. A dead battery prevents the thermostat from communicating with your furnace or heat pump.
2. Check the Air Filter
A clogged hvac air filter is the number one cause of furnace failure. It restricts airflow, causing the system to overheat and trip a safety limit switch, effectively shutting off the burners.
- Action: Inspect the filter. If it looks grey, brown, or clogged, replace it immediately. This easy step can restore heat within minutes.
3. Verify System Power
Electrical and fuel issues are common causes of a complete heating failure. Check both your home’s circuit panel and the physical gas valve to verify the system has power and fuel.
- Breaker Panel: Check your main electrical panel. If the breaker labeled for your Furnace or Air Handler is tripped (in the middle or off position), flip it firmly to OFF, then back to ON. If it immediately trips again, call a pro immediately.
- Gas Valve: If you have a gas furnace, ensure the manual gas valve on the pipe leading to the unit is open (handle parallel to the pipe).
System-Specific Problems and Solutions
If the initial checks don’t work, the failure is specific to your equipment type.
Gas HVAC Not Blowing Hot Air
If your gas furnace fan is running but the air is cold, the system is failing to ignite gas or detect the flame.
| Problem/Cause | What’s Happening | When to Call a Pro (Immediate) |
| Ignition Failure | The electronic ignitor or pilot light fails to light the gas. The system shuts down for safety. | Call Pro: This requires replacing a faulty ignitor or control board. |
| Dirty Flame Sensor | The sensor can’t detect the flame, causing the furnace to think the gas didn’t light. | Call Pro: A technician must carefully clean or replace this critical safety sensor. |
| Noisy Start/Shut Down | You hear a faint click and whirring, but the furnace never blows warm air. | Call Pro: Indicates a failure of the blower motor or gas valve. |
Electric HVAC Not Blowing Hot Air
If your electric furnace is blowing cool air, the heating coils are not receiving power or are damaged.
| Problem/Cause | What’s Happening | When to Call a Pro (Immediate) |
| Coil Failure | One or more electric heating elements (coils) have burned out and are not producing heat. | Call Pro: Requires testing and replacement of the coils or sequencers. |
| Sequencer Failure | This device controls power to the heating elements. If it fails, the elements won’t turn on. | Call Pro: The sequencer must be replaced to restore heat. |
| Second Breaker Tripped | Electric furnaces often use two separate breakers; one for the blower and one for the coils. | Check Breaker Panel: Ensure both breakers are fully reset. |
Heat Pump Not Blowing Hot Air
A heat pump failure often involves the outdoor unit or internal valves. (Note: If your system is blowing cold in summer and won’t cool, this points to the same components, resolving the concern of HVAC only blowing hot air when the season changes.)
| Problem/Cause | What’s Happening | When to Call a Pro (Immediate) |
| Reversing Valve Stuck | The valve that switches the system between heating and cooling is stuck in the cooling position. | Call Pro: Technician must repair or replace the reversing valve. |
| Signs of Low Refrigerant | A leak means the unit can’t absorb enough heat from the outdoor air. | Call Pro: The leak must be found, repaired, and the system recharged. |
| Thick Ice on Outdoor Unit | The defrost system failed, or airflow is blocked, preventing the unit from absorbing heat. | Call Pro: Indicates a sensor or control board failure. |
When to Contact a Professional
Do not attempt electrical or combustion repairs yourself. Call Meyer Heating & Air immediately if you encounter any of the following:
- You smell gas (rotten eggs) or electrical burning. Turn the unit off at the breaker and call immediately.
- The breaker trips repeatedly after you reset it.
- The furnace has no power even after checking all switches and breakers.
- The fan runs, but the furnace won’t ignite after checking the filter.
Need Heating Assistance Today? Contact Meyer Heating & Air
When your comfort is compromised, trust the experts. Our certified technicians are available to provide professional furnace repair and heat pump repair quickly and safely. We diagnose issues with all types of systems, whether gas, electric, or heat pump.
Contact Meyer Heating & Air today for reliable service in the St. Louis, MO area.