“Why is my air conditioner not blowing hot air?” If your system is a standard air conditioner, it is designed to cool, not heat. It will not blow hot air. However, if you have a heat pump, which looks like an air conditioner outside but can also provide heat, or a furnace inside your home, then it should blow hot air when you need warmth. This article explains why your heating system might not be working when it should. We will cover the common causes for no heat HVAC, what to do if your thermostat set to heat but no heat, why a heat pump blowing cold air is a problem, issues like a furnace not turning on, and general HVAC system troubleshooting no heat tips.
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Getting Started: What System Do You Have?
The first step to fixing your heating problem is knowing what kind of system you have. Many people use the term “air conditioner” loosely. They might mean the big box outside their house. That outdoor box is part of the system.
Heat Pumps: Both Cool and Heat
A heat pump is a single system that can cool your home in the summer and heat it in the winter. It moves heat instead of making it. In summer, it takes heat from inside your house and moves it outside. In winter, it takes heat from the air outside (yes, even cold air has some heat) and moves it inside your house. The outdoor unit looks very much like an air conditioner. This is why people often get them confused. If you have one system that does both cooling and heating, you likely have a heat pump.
Furnaces: Just for Heating
A furnace is a heating-only system. It is usually inside your house, often in a basement, closet, or attic. Furnaces make heat by burning fuel. This fuel can be natural gas, propane, oil, or electricity. Furnaces work with an air conditioner’s indoor coil and blower for cooling in the summer, but they only heat in the winter.
So, if you expect hot air, you either have a heat pump trying to heat or a furnace trying to heat. A regular air conditioner just won’t do it.
First Steps: Simple Checks You Can Do
Before you call a professional, there are some easy things you can check yourself. These common issues often cause no heat HVAC problems.
Checking the Thermostat
The thermostat is your system’s brain. It tells the heat pump or furnace what to do.
* Is it On? Make sure the thermostat has power. Some use batteries; check if they need changing.
* Is it Set Correctly? Check the mode. Is it set to “Heat”? Or is it on “Cool,” “Auto,” or “Off”? Make sure it’s on “Heat.”
* Is the Temperature Right? Is the setting higher than the temperature in the room? The system won’t start if the room is already warm enough. Turn the set temperature up by 5 degrees or more to test it.
* Fan Setting: Is the fan set to “Auto” or “On”?
* Auto: The fan runs only when the system is heating or cooling. This is the normal setting for saving energy.
* On: The fan runs all the time, whether the system is heating or not. If the system isn’t heating, an “On” setting will just blow room-temperature or even cold air. Make sure it’s on “Auto.”
* Programmable Thermostats: If you have a programmable thermostat, check the schedule. Is it set to turn the heat on at the right time? Has it somehow been programmed to stay off?
* Reset: Some thermostats can be reset. Check the manual for how to do this. Sometimes a simple reset fixes glitches.
If your thermostat set to heat but no heat and everything seems right on the thermostat itself, the problem is likely with the heating system or wiring, not the thermostat.
Looking at Power
Heating systems need power to run. No power means no heat.
* Check the Circuit Breaker: Go to your main electrical panel. This box is usually in the basement, garage, or a utility closet. Look at the switches. Each switch controls power to a part of your house. Find the breaker labeled for your furnace or heat pump.
* Is the switch in the “On” position?
* Is one switch pointing to the middle? This means it has tripped. Flip it firmly all the way to the “Off” position first. Then flip it back to the “On” position.
* For heat pumps, check the breaker for the outdoor unit too. There might be one near the unit itself or inside on the main panel.
* Check the Emergency Shut-Off Switch: Furnaces often have a power switch near the unit. It looks like a regular light switch. It’s usually on the furnace itself or on a wall nearby. Make sure this switch is in the “On” position. Sometimes people turn this off by mistake, thinking it’s a light switch.
* Pilot Light (Gas Furnaces): If you have an older gas furnace, check the pilot light. This is a small, constant flame that ignites the main burners. If it’s out, the furnace won’t heat.
If a breaker trips again right after you reset it, there is a serious electrical problem. Do not keep resetting it. This points to an issue that needs a professional. A tripped circuit breaker tripped furnace/heat pump is a common reason for the system not to run.
Deciphering Specific Heating Problems
Once you’ve done the simple checks, you can look at more specific issues. These depend on whether you have a furnace or a heat pump.
When the Blower Stops
The blower motor is a big fan inside your system. It pushes the warm air through the ducts and into your rooms. If the blower motor not working, you won’t feel any air coming from the vents, even if the system is making heat.
* Causes:
* Bad motor: The motor itself can burn out or fail.
* Bad capacitor: The capacitor helps the motor start. If it’s bad, the motor might hum but not start.
* Control board issue: The main control board tells the blower when to turn on. A problem with the board can stop the blower.
* Safety switch tripped: Sometimes the blower stops because another part of the system is too hot or has a problem, triggering a safety switch.
* What to Check:
* Listen for sounds. Can you hear the motor trying to start? Or is it totally silent?
* Check the control board lights (if your unit has them). Flashing lights often show error codes related to specific problems, like the blower.
* Fix: Blower motor problems usually need a technician. Replacing a motor or capacitor involves electrical wiring and technical know-how.
Furnace Ignition Troubles
For gas or oil furnaces, making heat involves lighting fuel. Problems with this lighting process mean your furnace not turning on or turning on briefly and then shutting off.
* Pilot Light Issues (Older Furnaces):
* If the pilot light is out, the furnace won’t start the main burners. You might be able to relight it yourself following the instructions on the furnace panel. Be very careful when working with gas. If you smell gas, do not try to relight it. Leave the area and call your gas company immediately.
* The thermocouple (a safety sensor that detects the pilot flame) can fail. If the thermocouple is bad, it won’t signal that the pilot is lit, and the gas valve will stay shut off as a safety measure.
* Electronic Ignitor Issues (Newer Furnaces):
* Modern furnaces use an electronic ignitor instead of a pilot light. This ignitor gets very hot or creates a spark to light the gas.
* If the ignitor is cracked or burned out (ignitor or pilot light issue), it won’t light the gas, and the furnace won’t heat.
* You might hear the furnace try to start (click sounds, maybe hear gas briefly) but fail to ignite. It might try a few times and then stop.
* Gas Supply: Make sure the gas valve to the furnace is open. It’s usually a handle on the pipe near the furnace. It should be in line with the pipe.
* Flame Sensor: After the gas ignites, a flame sensor confirms that the burners are lit. If this sensor is dirty or faulty, it might think there’s no flame and shut off the gas as a safety. This can cause the furnace to cycle on and off quickly.
Issues related to gas or ignition should always be handled by a qualified HVAC technician. Gas is very dangerous if not handled correctly.
Heat Pump Heating Failures
Heat pumps work differently than furnaces. If your heat pump blowing cold air when it should be heating, there are specific parts to check.
* Reversing Valve: As mentioned before, this valve switches the heat pump between heating and cooling mode. If the reversing valve failure heat pump occurs, it might get stuck in cooling mode, causing the heat pump blowing cold air indoors.
* Symptom: The outdoor unit is running, the fan is blowing inside, but the air feels cool instead of warm.
* Fix: Replacing a reversing valve is a complex job for a professional.
* Defrost Cycle: In cold weather, the outdoor coil of a heat pump can ice up. Heat pumps have a defrost cycle to melt this ice. During defrost, the system stops heating your home and may even blow cool air for a short time (often the auxiliary heat kicks in during defrost). This is normal. However, if the defrost cycle isn’t working correctly, the unit can become covered in thick ice, stopping it from heating.
* Symptom: Heavy ice buildup on the outdoor unit coil.
* Fix: A technician needs to diagnose why the defrost cycle isn’t working.
* Auxiliary Heat: Heat pumps use auxiliary heat not working (also called emergency heat or backup heat) when the outside temperature is very cold or during the defrost cycle. This is usually electric resistance heat (like a giant toaster coil) or sometimes a furnace paired with the heat pump.
* Symptom: Your heat pump runs, but the house isn’t getting warm, especially when it’s very cold outside, and the air coming out isn’t very hot, or the “Emergency Heat” light is on but no warm air comes out.
* Causes for auxiliary heat not working: Blown fuses or tripped breakers for the auxiliary heat strips, problem with the heating elements themselves, issue with the control board or relays that turn on the auxiliary heat.
* Fix: Check the specific breakers for the auxiliary heat. If those are fine, a technician needs to diagnose the heating elements or controls. Auxiliary heat uses a lot of electricity, so it’s expensive to run all the time, but it’s necessary when the heat pump alone can’t keep up.
* Low Refrigerant: Heat pumps move heat using refrigerant. If the refrigerant level is low (due to a leak), the system can’t move heat well. This means it won’t cool well in summer and won’t heat well in winter.
* Symptom: System runs but doesn’t heat or cool properly. Ice might form on coils (indoor coil in heating mode, outdoor coil in cooling mode). Hissing or bubbling sounds might be heard.
* Fix: Finding and fixing a refrigerant leak, then recharging the system, requires a certified technician.
Airflow Blockages
Sometimes the heating system is working fine, but the warm air can’t get into your rooms.
* Dirty Air Filter: A clogged filter is one of the most common reasons for poor airflow and system problems. A dirty filter blocks air moving into the furnace or heat pump. This makes the system work harder, can cause it to overheat and shut down, and reduces the amount of warm air reaching your rooms.
* Check: Find your air filter (usually near the furnace or air handler, sometimes in a return vent). Pull it out. Hold it up to the light. Can you see light through it? If not, it’s dirty and needs changing.
* Fix: Replace the dirty filter with a clean one of the correct size. Change filters regularly (check the filter packaging or manual for how often, usually every 1-3 months).
* Blocked Vents: Make sure the supply vents in your rooms are open and not blocked by furniture, rugs, or curtains. Also, check return vents (where air is pulled back into the system) are not blocked.
* Blocked Flue or Chimney (Furnaces): Gas or oil furnaces produce exhaust fumes. These fumes must safely exit through a flue pipe and chimney. If the flue is blocked (e.g., by a bird’s nest, debris), the furnace has safety switches that will prevent it from running to avoid dangerous carbon monoxide buildup.
* Symptom: Furnace won’t run, or runs briefly and stops.
* Fix: Blocked flues are serious and need a professional to clear.
When to Call a Pro
While you can check the thermostat, breakers, and air filter, many heating problems need professional help. Call an HVAC technician if:
* You smell gas (leave the area immediately).
* A circuit breaker trips repeatedly.
* You hear strange noises (grinding, banging, loud humming).
* You see ice buildup on the outdoor unit of a heat pump that doesn’t go away after a short time.
* You suspect a problem with the ignitor, pilot light, flame sensor, blower motor, or reversing valve.
* You think there might be a refrigerant leak.
* You have checked the simple things, and the system still doesn’t work.
* You are not comfortable working near electrical parts or gas lines.
Dealing with common causes for no heat HVAC often involves parts you shouldn’t try to fix yourself.
Keeping Your System Running
Preventative maintenance is key to avoiding heating problems in the first place.
* Regular Filter Changes: This is the easiest and most important thing you can do.
* Annual Check-Up: Have a qualified HVAC technician inspect your system every year before the heating season starts. They can clean parts, check for wear and tear, lubricate moving parts, check refrigerant levels (for heat pumps), and make sure safety controls are working. This can catch small problems before they cause a full breakdown and are a critical part of HVAC system troubleshooting no heat.
* Keep Outdoor Units Clear: Make sure the outdoor unit of a heat pump is free of leaves, snow, ice, and other debris. Don’t let shrubs or plants grow too close to it.
Taking care of your system helps it run better, last longer, and reduces the chances of waking up to a cold house.
Troubleshooting Summary Table
Here is a quick guide to common no-heat issues:
| Symptom | Possible Problem | System Type | Easy Check? | Pro Needed? | LSI Keyword Covered |
|---|---|---|---|---|---|
| No heat at all | Thermostat setting wrong | Both | Yes | No | thermostat set to heat but no heat |
| No heat at all | Power off (breaker tripped) | Both | Yes | Maybe | circuit breaker tripped furnace/heat pump |
| No heat at all | Emergency shut-off switch off | Furnace | Yes | No | |
| No air from vents | Blower motor not working |
Both | No | Yes | blower motor not working |
| Furnace tries to start, stops | Ignitor or pilot light issue |
Furnace | Limited | Yes | ignitor or pilot light issue, furnace not turning on |
| Furnace tries to start, stops | Flame sensor dirty/bad | Furnace | No | Yes | furnace not turning on |
| Furnace no start, no sound | Gas valve shut off | Furnace | Yes | Maybe | furnace not turning on |
| Heat pump blowing cold air | Reversing valve failure heat pump |
Heat Pump | No | Yes | Heat pump blowing cold air, reversing valve failure heat pump |
| Heat pump runs, not warm air | Low refrigerant | Heat Pump | No | Yes | Heat pump blowing cold air |
| Heat pump runs, not warm air | Ice buildup on outdoor unit | Heat Pump | Limited | Yes | Heat pump blowing cold air |
| Heat pump runs, not warm air | Auxiliary heat not working |
Heat Pump | Limited | Yes | auxiliary heat not working |
| Weak airflow / unit cycles off | Dirty air filter | Both | Yes | No | common causes for no heat HVAC |
| Weak airflow | Blocked vents | Both | Yes | No | common causes for no heat HVAC |
Answering Common Questions
Here are answers to some frequent questions about heating systems not working.
Q: My thermostat set to heat but no heat, what’s the most likely simple cause?
A: For both furnaces and heat pumps, the most common simple cause is a tripped circuit breaker or a clogged air filter. Check those first after making sure your thermostat is set to heat and the temperature is high enough.
Q: My heat pump is blowing air, but it feels cool, not cold. Is that normal?
A: A heat pump heats differently than a furnace. A furnace heats air very hot (often 130-140°F). A heat pump heats air to a lower temperature (often 85-100°F). The air might not feel “hot” like furnace air, especially on a cold day. It might feel warm, or even slightly cool compared to your hand temperature, but it should feel warmer than the room air. If it feels the same as room air or colder, there’s likely a problem like low refrigerant or a stuck reversing valve, leading to heat pump blowing cold air.
Q: My furnace makes a clicking sound but doesn’t start. What is that?
A: The clicking sound is often the electronic ignitor trying to spark and light the gas. If it clicks but no flame appears, the ignitor itself might be faulty (ignitor or pilot light issue), the gas isn’t reaching it, or the flame sensor is bad.
Q: Can I use my emergency heat all the time?
A: You can use emergency heat, but it’s very expensive. Emergency heat (auxiliary heat not working if it’s broken) uses electric resistance, which uses a lot more electricity than a heat pump or furnace. It’s meant for temporary use when the heat pump can’t keep up or needs repair.
Q: How often should I change my air filter?
A: It depends on the filter type (1-inch filters need changing more often than thicker ones) and how much you use your system. A good rule is to check 1-inch filters monthly and change them if they look dirty (can’t see light through them). Thicker filters might last 3-6 months. A dirty filter is a big common cause for no heat HVAC because it restricts airflow.
Q: Is it safe to try and fix a furnace myself?
A: Only attempt very simple things like checking the thermostat, breakers, or air filter. Do not attempt repairs involving gas lines, electrical components beyond resetting a breaker, or internal furnace parts like ignitors or flame sensors. Gas leaks and electrical shocks are serious risks. HVAC system troubleshooting no heat that goes beyond basic checks should be left to trained experts.
Q: Why would my circuit breaker tripped furnace/heat pump?
A: A breaker trips to stop power when there’s a problem that could be dangerous. Common reasons include:
* The motor (blower or compressor) is drawing too much power because it’s old or struggling.
* Wiring issues (short circuit).
* Overloaded circuit (though less common for the main HVAC breaker).
* A failing component elsewhere in the system (like a bad heating element in auxiliary heat) causing an overload.
If it trips once and resets fine, it might have been a temporary issue. If it trips again, call a technician right away.
In Conclusion
If your home is cold and your heating system isn’t blowing warm air, don’t panic. First, figure out if you have a furnace or a heat pump. Then, go through the simple checks: thermostat settings, power (breakers, emergency switch), and air filter. These steps fix many problems. If those checks don’t work, the issue is likely a specific part failure, like a blower motor not working, an ignitor or pilot light issue, or a reversing valve failure heat pump. For these more complex problems, or if you smell gas or see repeated tripped breakers, it’s time to call a qualified HVAC professional. Regular maintenance can help prevent many of these issues and keep your home warm when you need it most.