> By: The Cooling Company > Published: 2025-12-20 > Last updated: 2025-12-20
If your heater won't turn on but your AC works, start with simple checks you can do safely tonight. Many issues are small and cause no heat even when the cooling side runs fine. Start by checking the thermostat mode, replacing batteries, verifying breakers, flipping the furnace power switch, and swapping in a clean air filter. These steps fix many.
Key Takeaways
- Check thermostat mode, batteries, breakers, service switch, and filter first.
- Heat and AC may use different circuits or controls. One can work while the other is dead.
- Heat pump, gas furnace, and electric heat issues differ and need different fixes.
- Call a licensed technician for gas leaks, repeated breaker trips, or control-board faults.
If those steps do not restore heat, make notes and take photos. Note sounds, lights, and any error codes you see on the furnace control board. That information helps a technician arrive with the right parts and avoids extra trips. For authoritative guidance on safe checks, see ASHRAE Technical Resources.
Where should you start troubleshooting?
Start with the items you can reach without special tools. The thermostat, the return air filter, the furnace service switch, and the breaker box are common causes of no-heat calls. Homeowners fix many problems by methodically checking these items. Take five to ten minutes and work through the list calmly.
Record what you see and hear. Set the thermostat mode to HEAT and raise the setpoint several degrees above the room temperature. Listen at the furnace for clicks, a spinning inducer, and the blower motor. Look for LED flash codes on the control board. Those codes give a technician a faster diagnosis.
Is the thermostat set correctly?
Ensure the thermostat is in HEAT mode and the set temperature is higher than the current room temperature. Some thermostats have an AUTO fan setting that only runs the fan when there is a call for heat. If the fan is set to ON, it may run without the heat engaging, which can be confusing.
Replace batteries if the display flickers or the thermostat acts oddly. Programmable schedules can override a manual call for heat. Clear any temporary holds or schedule settings before testing. If the thermostat appears dead after a battery swap, note that for the technician.
Have you checked the circuit breakers?
Open your service panel and find breakers labeled Furnace, Air Handler, or Outdoor Unit. A tripped breaker can kill only the heating side of the system. Reset any tripped breaker once, then test the system again to see if heat returns.
If a breaker trips again immediately or soon after, do not keep resetting it. Repeated trips point to an electrical fault, a failing motor, or a shorted element. Call a licensed electrician or HVAC technician to diagnose the cause safely.
Is the furnace power switch on?
Most furnaces have a service switch that looks like a household light switch on or near the unit. If that switch is OFF, the furnace and its control board are powerless even when the AC works. Flip it ON and place another call for heat after a short wait.
Some systems also have a disconnect at the air handler or a fuse inside the furnace cabinet. Inspect visible switches and replace blown fuses if you are comfortable doing so. Technicians confirm these simple items on arrival to avoid wasted diagnostic time.
heater won't turn on but ac works: identifying your HVAC type
Knowing what kind of heating system you have narrows likely causes and makes your checks safer. Gas furnaces, electric furnaces, and heat pumps fail in different ways. Look at the outdoor unit, the presence of a gas pipe, and how the vents are arranged to decide which path to follow.
Heat pumps run both heating and cooling modes and rely on the outdoor unit to move heat. Gas furnaces use combustion, a gas supply, and venting. Electric furnaces use high-voltage heating elements. Recognizing the system helps you avoid unsafe DIY work and gives better data to the technician.
How do gas furnace failures present?
Many gas furnace issues show as no ignition after you hear the inducer motor run. You may hear the inducer spin, then a click, and then no flame. A failed hot surface ignitor or a dirty flame sensor often causes that pattern.
If you smell gas, leave the house immediately and call emergency services or your gas company. Do not try to relight pilots or work on gas components yourself. Combustion system work carries serious risks and must be done by a licensed professional.
What to check on electric furnaces or heat strips?
Electric furnaces and strip heaters rely on high-voltage elements to make heat. If one or more elements burn out, the blower may still operate but the system will not produce heat. You may also see breakers tripped in the main panel when elements fail.
Replacing elements or high-voltage fuses is a job for a trained technician. These parts run at dangerous voltages. Avoid DIY replacement unless you have proper training and safety gear. Call a professional to test and replace elements safely.
How do heat pump issues differ?
Heat pumps move heat using refrigerant and need the outdoor unit to run in heating mode. If the outdoor unit does not start, the system will not heat. Ice buildup on the outdoor coil or a stuck reversing valve can also make the system blow cool air.
Heat pumps enter short defrost cycles that may blow cool air briefly. If the unit stays in defrost or the outdoor coil is heavily iced, there may be a defrost control or sensor fault. Refrigerant or compressor problems also reduce heating output and need certified service.
What safe DIY checks can you try tonight?
Do low-risk checks that often restore operation quickly. Thermostat mode, fresh batteries, filter condition, labeled breakers, and the furnace service switch are easy to inspect. These steps require no special tools and keep you safe while ruling out common causes.
Always prioritize safety. If you detect a gas smell, repeated breaker trips, or need to open live electrical panels, stop and call a licensed technician. These checks do not replace professional service when there are combustion, electrical, or sealed-system issues.
Can you toggle the thermostat power?
Turning the thermostat off and then on again can clear small software glitches. Many digital thermostats include a restart option in their settings menu. Try that first to see if the control will reset and resume normal operation.
If the thermostat shows no power, check fresh batteries and the common (C) wire. A missing or loose C wire can cause odd behavior. For wiring changes or upgrades, contact a technician to avoid damaging the thermostat or system.
Should you replace the thermostat batteries?
Many line-voltage thermostats use AA or AAA batteries. Low batteries can produce odd displays and interrupt the signal to the furnace. Replace batteries with fresh cells and then set the thermostat to HEAT and raise the setpoint to test.
If the system starts after a battery change, the batteries were likely the cause. If batteries die quickly, ask a technician about adding a C wire for stable power. That upgrade reduces future failures and keeps the thermostat powered.
Will resetting the breaker help?
A single breaker reset may restore power to a tripped furnace or air handler. Open your panel, find the tripped breaker, and move it fully OFF and then ON. Stand to the side and keep hands away from bare bus bars when working in the panel.
If the breaker trips again immediately, stop and call a professional. Repeated trips indicate an electrical problem that could be dangerous. Do not tape or force a breaker to stay on; that creates a safety hazard.
Can you clean or swap the air filter?
Turn off the furnace and remove the return filter. If the filter is dark and loaded, replace it with the correct size and rating. A clogged filter can block airflow and trip the furnace high-limit switch, stopping heat output.
A clean filter restores airflow and reduces stress on the blower motor. Replace filters on a regular schedule, often every 30 to 90 days. Good airflow prevents many no-heat calls and extends the life of the equipment.
Should you inspect the furnace door and service switch?
Make sure the furnace access panel is fully seated and latched. Many units have an interlock switch that stops operation if the door is loose or removed. Also verify the service switch near the unit is ON.
If you find the switch OFF, flip it ON and test for heat. Loose panels or off switches are a common reason for no-heat calls. Do not operate the unit with panels removed; only inspect and then restore the panel before restarting.
Is the flame sensor dirty and fixable?
A flame sensor coated in soot or film can cause the burners to shut off shortly after they ignite. The control board senses no flame and closes the gas valve as a safety measure. Cleaning the sensor often restores normal ignition.
Cleaning requires removing the furnace access panel and gently rubbing the sensor rod with fine steel wool or emery cloth. Always cut power and gas as directed by the unit manual before working inside. If cleaning does not help, the sensor may need replacement.
Could a clogged condensate switch stop heating?
High-efficiency furnaces and some air handlers use a condensate pan and a float or pressure switch to detect drainage. If the pan is full or the drain is blocked, the switch will prevent the unit from running. Check the pan for standing water and clear the drain.
Many homeowners clear the drain with a wet-vac or a mild bleach solution to remove algae. If drainage problems continue, call a technician. Persistent clogs may indicate a failed pump or installed drain problem.
Could controls or wiring cause no heat?
Control and wiring faults often affect only one side of the system. A burned relay, a bad transformer, or a loose thermostat wire can stop the heat while the AC still works. These faults need safe testing with a multimeter and diagnostic skill.
Technicians test 24VAC control voltage at the thermostat, the control board, and contactors. They also inspect fuses and high-voltage parts. If you suspect control or wiring faults, gather photos and notes so the technician arrives prepared.
What if the transformer or control board is dead?
A weak or failed transformer can kill the 24VAC control power that runs the thermostat and relays. Symptoms include a dead thermostat display, no relay clicks at the board, or erratic control behavior. Testing requires a multimeter and knowledge of safe voltages.
Replacing a transformer or control board is a technical job. A licensed tech will match voltages and verify proper grounding. Avoid guessing with replacement parts; using the wrong component can cause more damage.
Could a bad relay or contactor stop heat?
Relays and contactors switch high-current circuits for compressors and electric heating elements. If a relay fails, the heater or outdoor unit may not energize. You may notice the absence of normal sounds or movement when calling for heat.
Visible damage such as burnt contacts suggests relay failure. Technicians routinely replace relays and will check coil voltages to confirm the control signal is present before swapping parts. That avoids unnecessary replacements.
Is the thermostat wiring intact at the control board?
Loose, corroded, or swapped wires at the control board can interrupt signals. Check that wires are secure and correctly labeled at both the thermostat and the furnace terminals. Take photos before you touch anything so you can restore original wiring if needed.
If wires are frayed or terminals show heat damage, call a technician. Rewiring requires the power off and proper tools. Proper connections eliminate intermittent faults and return reliable control.
How to test the limit switch or safety sensors?
Limit switches stop heat when the furnace overheats. Testing a limit switch involves reading resistance with a multimeter and comparing the result to the expected range in the service manual. This testing is best left to trained technicians.
Never bypass safety switches. Bypassing creates dangerous operation and may void warranties. If a limit switch trips, find the root cause such as blocked airflow or a failing blower motor before replacing the sensor.
When should you stop DIY and call a pro?
Stop do-it-yourself work for any gas smell, repeated breaker trips, or tasks involving high voltage or refrigerant. Those issues carry serious safety risk and require licensed tradespeople. A professional keeps repairs safe and code compliant.
Also call a technician for suspected heat exchanger cracks, sealed-system refrigerant work, or major control-board faults. These repairs need special tools and certifications. Proper diagnosis prevents wasted parts and repeat visits.
Need HVAC service help in Las Vegas?
If you're facing an HVAC emergency in Las Vegas, Henderson, or North Las Vegas, The Cooling Company offers fast, reliable service from licensed technicians. We understand that heating and cooling emergencies don't wait for business hours.
Call us now at 17029308411 for emergency service. Our team is ready to help restore your comfort quickly and safely.
What emergency safety risks should you know?
Gas furnaces can produce carbon monoxide if venting fails or combustion is incomplete. Symptoms include headache, dizziness, and nausea. Install and test CO alarms monthly. If an alarm sounds, evacuate and call emergency services.
Never ignore burning smells or visible flame rollout. These signs require evacuation and professional inspection. Safety always takes priority over saving time or money when combustion appliances act unsafe.
How to document problems for service calls?
Take clear photos of wiring, LED codes, and thermostat wiring. Note the exact time the problem began and what you tested. Record sounds, smells, and any steps you tried to reset the system.
Bring this documentation to the technician. It shortens diagnostic time and can reduce service cost. Good notes also help with warranty claims and follow-up questions after the repair.
Schedule service and next steps
If simple checks do not restore heat, plan for professional service. Leave power on so technicians can test the system in place. Keep a list of observed symptoms, LED codes, and which DIY steps you tried to speed repairs and avoid repeat visits.
For local homeowners, choose a company with good reviews and proper licensing. A local technician often arrives faster and may bring common parts. Outside your area, gather photos and error codes and choose a certified local tech ahead of the visit.
Las Vegas area service: call The Cooling Company at 17029308411
For readers in Las Vegas, Henderson, or North Las Vegas, call The Cooling Company at 17029308411 for prompt help. Our licensed HVAC technicians diagnose furnaces, heat pumps, and packaged units. We offer same-day or next-day service when possible and explain findings and options clearly.
Technicians inspect thermostats, breakers, ignition systems, reversing valves, and ductwork. They provide a written estimate and discuss repair versus replacement. Call 17029308411 to schedule service in Las Vegas, Henderson, or North Las Vegas.
If you are outside our area: find a NATE-certified pro
If you live outside our service area, find a NATE-certified technician via the NATE directory. Gather photos, error codes, and notes before the visit. That prep saves time and helps the technician order parts in advance.
For all homeowners, schedule preventive fall maintenance to reduce winter failures. A seasonal tune-up finds worn parts, checks combustion, and balances airflow. Preventive care lowers the chance of emergency repairs and extends equipment life.
Final quick checklist to try tonight
Set the thermostat to HEAT and raise the setpoint several degrees above room temperature. Replace thermostat batteries if needed and put in a clean air filter. Check labeled breakers and make sure the furnace service switch is ON. These steps fix many no-heat calls quickly.
If heat still fails after these checks, gather photos and notes and schedule service. If you smell gas or a carbon monoxide alarm sounds, leave the house immediately and call emergency services. Otherwise, call The Cooling Company at 17029308411 if you are local, or find a NATE-certified technician near you.
About The Cooling Company
- Phone: 17029308411
Sources and compliance notes
This aspect deserves careful consideration as you evaluate your options. Understanding the details helps you make more informed decisions. Consulting with qualified professionals provides additional insights specific to your situation. Take time to consider how this information applies to your particular needs and circumstances. Making well-informed choices typically leads to better long-term outcomes and greater satisfaction.
- ASHRAE Technical Resources: ASHRAE Technical Resources
- Find NATE-certified technicians: NATE directory
Critical compliance note: Do not attempt combustion, high-voltage, or refrigerant repairs yourself. Stop and call a licensed professional for gas smells, repeated breaker trips, or control-board faults.