HVAC Repair in O'Fallon, MO
Homes here need heat from October through April and cooling from May through September. If your system quits, tell us what it's doing and a licensed contractor who covers St. Charles County will get in touch.
Tell us about the job
It takes about a minute.
St. Charles County puts your system to work most of the year
Your furnace runs October through April here, and your air conditioner takes over for the five months after that. There is almost no season where the system gets to sit idle. On winter nights that average 25°F, the burner cycles on and off again and again to hold the house steady. That kind of repeated firing wears on the igniter and the ignition control over time, and when one of them fails, the house goes cold instead of warm.
Summer runs the other direction. Afternoons averaging 87°F keep the compressor working hard for months, and that steady load is what tends to wear down a capacitor or push a refrigerant leak into a real problem. St. Charles County has also seen 84 damaging wind events and 9 winter storms over the past ten years, and with almost one in five Missouri households losing power for a full day or more in 2024, a storm can knock out a system that was running fine right before the lights went out.
- 7 months
- October through April, your system heats
- 5 months
- May through September, it cools
- 25°F
- the average winter night it heats against
- 87°F
- the average summer afternoon it cools against
NOAA nClimDiv, 1991–2020 normals
A new furnace and air conditioner would cut about $210 a year off heating and cooling for a typical St. Charles County home.
Estimates for a typical St. Charles County home, compared with an older unit built to the previous federal minimum, from EIA household energy data, Missouri fuel prices and NOAA climate normals. Your home will differ.
Repair makes sense when one part has failed.
Replacement makes sense when the furnace's heat exchanger is cracked, the air conditioner's compressor has failed, or repairs keep coming.
- Why is my heat not working?
- Start with the thermostat. Make sure it is set to heat and the temperature is set above room temperature, since a setting bumped a degree or two can look like a dead furnace. If that is not it, check the breaker and any switch near the furnace that looks like a light switch, since that cuts power to the whole unit. Gas furnaces also need the pilot lit or the igniter working, so if you hear the blower run but get no heat, that is worth mentioning to whoever comes out. With winter nights here averaging 25°F, a furnace that is short cycling or blowing cold air is not something to leave for later.
- Why is my system running but not cooling the house?
- The most common reason is a dirty air filter choking off airflow, so check that first since it is the one thing you can fix yourself. A clogged filter starves the coil of air, and over time that can freeze the coil, which makes the problem worse even though the system is running. Outside, make sure the condenser unit has clear airflow on all sides and is not buried in leaves or grass clippings. If the filter is clean and the outdoor unit looks fine but the air coming from the vents is not cold, the system likely needs a contractor to check refrigerant levels or the compressor, since those are not things to diagnose yourself.
- What can I check before calling for HVAC repair?
- Check the thermostat settings first, including the batteries if it uses them, since a dead thermostat display can look like a dead system. Next check the breaker panel for a tripped breaker and any power switch near the indoor unit or furnace. Look at the air filter and replace it if it is visibly dirty, since restricted airflow causes problems in both heating and cooling. If the outdoor unit is not running, make sure nothing is blocking it and that it has power. Anything beyond this, like unusual noises, burning smells, or a system that will not turn on at all, is worth describing to a contractor rather than investigating further yourself.