Alton, IL HVAC Repair: Heater Runs but No Heat?

When your HVAC is turning on but no heat comes out, it is stressful in a St. Louis snap freeze. This guide shows how to diagnose the most common causes, what you can safely fix, and when to call a pro. If you need fast help, we offer 24/7 emergency HVAC repair and you can save with our $55 repair coupon. Use this to get warm again today without guesswork or wasted time.

First Things First: Safety and Quick Checks

Before you dive in, remember that HVAC equipment involves electricity, gas, and high temperatures. If you smell gas or see scorch marks, turn off the system and call a professional immediately.

Start with these basic checks that solve many no-heat calls:

1. Thermostat settings
   • Set to Heat, not Auto or Cool.
   • Raise the setpoint at least 3 degrees above room temperature.
   • Replace batteries if the screen is dim or blank.
2. Power and switches
   • Confirm the furnace switch is On. It often looks like a light switch near the unit.
   • Check the breaker. If it is tripped, reset it once. If it trips again, call for service.
3. Air filter
   • A clogged filter can cause overheating and safety lockouts. Replace it if it is dirty.
4. Vents and returns
   • Open supply registers and make sure returns are not blocked by furniture or rugs.

"Air Comfort is easy to work with, reliable and efficient. Exactly what you want in AC maintenance/repair."

Common Reasons Your HVAC Blows Cold Air in Heat Mode

Several issues can cause a blower to run while the house never warms up. Here are the most frequent culprits and how to navigate each.

1) Incorrect Thermostat or Mode Conflicts

Smart thermostats can misinterpret system type or staging. A heat pump set as conventional heat may call for the wrong equipment. Fan On instead of Auto can also push unheated air.

What to try

• Confirm system type in the thermostat settings: heat pump vs furnace.
• Set the fan to Auto so it runs only with a heat call.
• If you recently changed Wi-Fi thermostats, re-run equipment setup.

Call a pro if

• The thermostat keeps losing configuration or power cycling.
• You have dual-fuel or multi-stage equipment that was never configured.

"Spencer was very professional and answered all of my questions. Thank you."

2) Ignition Failure in Gas Furnaces

If the blower runs but the burners do not light, you may have a failed hot surface ignitor, a dirty flame sensor, or a gas valve issue. Modern furnaces lock out if they fail to ignite after several tries.

What to try

• Look for the viewing port. If you do not see a steady flame during a heat call, the furnace is not firing.
• Power cycle the furnace at the switch. Sometimes this clears a soft lockout.

Call a pro if

• You see repeated cycles of clicking without flame.
• You smell gas or see error codes flashing on the control board.

Our technicians clean flame sensors, test ignitor resistance, verify gas pressure, and check safeties to restore reliable ignition.

"Very positive. Called early today to report furnace stopped working. Antonio was here quickly and found issue and repaired. He was friendly and very competent."

3) Tripped High-Limit or Overheating From Airflow Problems

Restricted airflow overheats the heat exchanger. The furnace safety switch opens, shutting off burners while the blower stays on to cool the cabinet. That feels like cold air.

What to try

• Replace dirty filters. Check every 30 days in winter.
• Open blocked registers, especially in rooms near exterior walls.
• Inspect return grills for dust mats and pet hair.

Call a pro if

• You replace the filter yet still get hot-cold-short cycles.
• The blower runs for minutes after burners shut off and never catches up. A pro will check static pressure, blower speed, duct restrictions, and coil cleanliness. Air Comfort Service also offers Aeroseal duct sealing if leakage is the root cause.

"Prompt, professional service. Positive & helpful attitude. Brandon was good at explaining everything and I really appreciate the extra step they go to to leave your home in clean order (like the shoe covers)!"

4) Heat Pump Running in Defrost or on Auxiliary Heat Only

In St. Louis winters, heat pumps may enter defrost mode, which can temporarily send cooler air. If the outdoor unit is iced over, performance drops fast.

What to try

• Inspect the outdoor unit. Light frost is normal. Heavy ice is not.
• Clear snow from the top and sides. Maintain at least 18 inches of clearance for airflow.
• Set thermostat to Emergency Heat only if advised. It can get you heat but raises utility costs.

Call a pro if

• The outdoor fan never spins or you hear loud grinding.
• The reversing valve is stuck or the defrost board is faulty. We diagnose refrigerant charge, defrost sensors, and control boards to get proper heating restored.

"Logan did a great job. Left us with a positive peace of mind."

5) Pilot, Flame Sensor, or Condensate Issues in High-Efficiency Furnaces

High-efficiency condensing furnaces produce water. A clogged condensate trap or frozen drain can trigger pressure switch errors. Likewise, dirty flame sensors cause nuisance shutdowns.

What to try

• Make sure PVC intake and exhaust pipes are free of obstructions at the exterior wall. Ice, leaves, or nests can block them.
• If you see water pooling near the furnace, turn it off and call for service.

Call a pro if

• You notice gurgling or repeated start attempts.
• Pressure switch error codes appear. We clear drains, verify combustion air, and test inducer performance.

"Michael W performed the scheduled HVAC system preventative maintenance service. Answered all questions, made recommendations in a very professional manner. Excellent service…"

6) Electrical or Control Board Faults

Loose low-voltage wiring, failed relays, or burnt traces on the control board can run the blower while locking out heat.

What to try

• If the breaker trips repeatedly, stop and call a professional.
• Avoid bypassing any safety switches.

What we do

• Inspect wiring, test transformer output, verify 24V signals from the thermostat, and read board error logs. If replacement is smarter than repair, we present transparent options, including free second opinions on big-ticket items like heat exchangers.

7) Ductwork, Insulation, and Home Performance Factors

Sometimes the furnace is firing but the heat never reaches your rooms. Leaky ducts in attics, basements, or crawl spaces waste energy. Missing insulation and unbalanced airflow leave bedrooms cold.

Fixes that work

• Seal and balance ductwork. Aeroseal can cut leakage dramatically.
• Add blown-in attic insulation to reduce heat loss.
• Test and adjust dampers to improve room balance.

Local insight

• Many St. Louis homes have older brick construction and additions with mixed duct sizing. We routinely correct comfort gaps in those spaces without replacing the entire system.

"As always, the service tech was polite, thorough, and explained what he was doing before actually doing it. He also petted my cranky but curious old cat. So, another positive experience."

DIY Fixes You Can Safely Try Today

These simple steps often restore heat quickly and safely.

1. Replace or remove the dirty filter and reinsert correctly with airflow arrow toward the furnace.
2. Verify thermostat is set to Heat and Fan set to Auto.
3. Power cycle the furnace at the service switch for 60 seconds.
4. Check the outdoor heat pump for snow buildup and gently clear it.
5. Confirm all supply registers and returns are open.

If these do not solve it, involve a professional to protect your equipment and your warranty.

When to Call a Professional Right Away

• Gas smell or repeated failed ignition attempts
• Breaker trips or visible burn marks
• Heavy ice on your heat pump or no outdoor fan movement
• Water around the furnace or gurgling sounds in a high-efficiency unit
• Error codes on the control board or thermostat that repeat after a reset

Air Comfort Service technicians are available 24/7. We service all brands and models, from residential furnaces and heat pumps to commercial rooftop units and chillers. Our goal is minimal downtime and a first-visit fix whenever possible.

How We Diagnose No-Heat Calls the Right Way

Expect a methodical process to avoid parts-chasing and repeat visits.

1. Verify complaint, thermostat settings, and filter condition.
2. Pull fault codes and live test calls at the control board.
3. Inspect ignition system, flame sensor microamps, gas pressure, and safeties.
4. Measure static pressure, temperature rise, and airflow.
5. For heat pumps, check refrigerant charge, reversing valve operation, and defrost logic.
6. Inspect ductwork, returns, and insulation where accessible.
7. Present clear repair options with upfront pricing and photos when helpful.

Two hard facts you can count on

• We have served Greater St. Louis since 1969 and are a Carrier Factory Authorized Dealer. That certification requires proven technician training and customer satisfaction.
• Our Preferred Partner Plan starts at $19 per month. It includes two annual system checks covering heating and cooling, priority scheduling, and 50 percent off after-hours emergency service fees, plus repair and equipment discounts.

"Tyler arrived a few minutes early and was very polite, professional and thorough. He is an asset to your company."

Prevent No-Heat Surprises With Proactive Maintenance

St. Louis winters swing from damp chill to deep freeze. Seasonal maintenance keeps your furnace and heat pump ready for both.

What a professional tune-up includes

• Clean and test flame sensor and ignitor
• Check gas pressure and combustion
• Verify heat exchanger condition and temperature rise
• Test safety controls and limit switch function
• Inspect blower wheel, motor amps, and belt condition where applicable
• Clear and prime condensate drains on high-efficiency models
• For heat pumps: test defrost cycle, reversing valve, and refrigerant charge

Member advantages

• Preferred Partner Plan members receive two system checks per year, priority scheduling, half off the standard $199 emergency dispatch fee, and repair discounts. If you pay monthly, your 12th month is free.

"Logan was absolutely awesome. Explaining every detail about our issue and the cost and trying to keep the cost down as much as possible - great person from a great company... Great job Bryce"

Repair vs Replacement: How We Help You Decide

We consider safety, cost, reliability, and comfort.

• Age and condition: Furnaces over 15 years with repeated failures may justify replacement.
• Repair cost ratio: If a repair is more than 30 percent of replacement on an older unit, we discuss long-term value.
• Comfort and air quality: If rooms stay cold or the system is loud, new equipment and duct improvements solve both heat and comfort.
• Efficiency: Heat pumps and furnaces with modern controls can reduce energy bills and improve winter comfort.

Free second opinions

• Get peace of mind on big repairs like compressors or heat exchangers. We provide a free second opinion so you can make a confident choice.

St. Louis Insight: What Fails Most When Temps Plunge

When we hit back-to-back cold snaps along the Missouri and Illinois rivers, we often see:

• Dirty flame sensors causing short heat cycles
• Clogged high-efficiency furnace drains freezing at exterior walls
• Heat pumps locked in defrost from snow drifts and leaf debris
• Old mercury thermostats drifting in cold hallway locations

A quick relocation of the thermostat, PVC vent re-route, or a drain heat trace can prevent future no-heat events. Our team pulls required permits for any venting adjustments and keeps your home protected with shoe covers and drop cloths during work.

Special Offers to Get Your Heat Back Fast

• Save $55 on any service repair. Use code 55REPAIR24. Limited time. Not valid with other offers. One per household.
• 24/7 Emergency Service: Standard dispatch fee $199. Preferred Partner Plan members pay $100.
• Members also save 15 percent on repairs. Expires 2026-11-04.

Call 314-814-8455 or schedule at https://www.aircomfortservice.com/ and mention code 55REPAIR24 to lock in your savings.

Frequently Asked Questions

Why does my furnace blow cold air sometimes, then warm air later?

Short burner cycles or a tripped high-limit switch can cool the air between heat calls. Replace a dirty filter and open registers. If it repeats, call for airflow and safety checks.

Can a thermostat cause no heat even if the blower runs?

Yes. Wrong system type, bad wiring, or a failing thermostat can run the fan without a heat call. Re-run thermostat setup and ensure Fan is set to Auto. Call if issues persist.

Is it safe to keep resetting my furnace when it will not ignite?

No. One power cycle is fine. Repeated lockouts point to ignition or gas issues. Stop and call a pro to avoid damage and ensure safe operation.

How long should a furnace heat up after it starts?

Most furnaces deliver warm air within 2 to 5 minutes. Longer delays suggest ignition, airflow, or control problems that need diagnosis.

Should I use Emergency Heat on my heat pump?

Use it only if the outdoor unit is iced or malfunctioning. Emergency Heat uses backup heat and increases bills. Clear snow and schedule a service visit.

Stay Warm, Stay Safe

If your HVAC is turning on but no heat comes out, start with the simple fixes above. When you need expert help, call the St. Louis team trusted since 1969. We handle all brands, offer 24/7 emergency service, and back our work with clear, upfront pricing. Mention code 55REPAIR24 to save $55 on repairs.

Ready for Fast Heat Restoration?

• Call now: 314-814-8455
• Schedule online: https://www.aircomfortservice.com/
• Save today: $55 OFF any service repair with code 55REPAIR24

Prefer VIP treatment? Join the Preferred Partner Plan starting at $19 per month for two annual system checks, priority scheduling, and 15 percent off repairs.

About Air Comfort Service, Inc.

Family owned and serving Greater St. Louis since 1969, Air Comfort Service, Inc. is a Carrier Factory Authorized Dealer and winner of Carrier President's Award honors. We are fully licensed and insured, offer 24/7 emergency service, and provide transparent pricing. Our Preferred Partner Plan members enjoy priority scheduling and repair discounts. We service all brands and handle residential and commercial systems, including rooftop units and chillers.