> By: The Cooling Company
If your house heater refuses to run, start with simple checks like thermostat mode, power, breakers, filters, condensate lines, and pilot or ignitor. Try safe DIY steps first to rule out easy causes. If you smell gas or carbon monoxide, evacuate and call emergency services and a licensed technician right away. (ASHRAE Technical Resources)
Key Takeaways
- Begin with the thermostat, power switch, circuit breaker, filter, and condensate drain.
- Never bypass safety switches or work on gas or wiring yourself.
- For gas smells, CO symptoms, or repeated ignition failures, evacuate and call a pro.
House Heater Not Turning on: Quick Fixes to Try
When your house heater will not turn on, start with a short, ordered checklist. These checks take little time. They help you learn whether the problem is the thermostat, the home's electrical supply, airflow, or the furnace itself. Walk the house and note which zones are cold and which registers feel warm. That will help narrow the cause before opening any covers.
The goal is to rule out common, low-risk causes first. Use fresh batteries in the thermostat, confirm mode and setpoint, check the service switch by the furnace, inspect the breaker or fuse, and glance at the air filter. If you find a tripped breaker or a filthy filter, fixing it often restores heat within minutes. Keep a notepad and record any error codes or unusual sounds.
Is the thermostat set to heat and above room temp?
The thermostat must be in HEAT mode and set higher than current room temperature to call for heat. Many digital thermostats have OFF or COOL settings that prevent a heat call. Also check the fan setting; if it is set to ON, the blower may run but the burner will not ignite. Correct mode and setpoint errors are a frequent cause of a no-heat condition.
If the thermostat looks normal but the furnace does nothing after you raise the setpoint, note the time and any delays. Most systems respond in under two minutes. Long delays or no response suggest the thermostat is not signaling the furnace or the furnace control board is timing out.
Are thermostat batteries fresh?
Some thermostats run on batteries only, or use batteries as backup. Weak batteries can cause intermittent operation or loss of settings. Replace AA, AAA, or coin-cell batteries and wait a minute for the thermostat to reboot. Batteries are inexpensive and often fix communication issues with the furnace.
If you have a smart thermostat, battery problems can also affect wireless connections and local control. After you change batteries, test the furnace by raising the setpoint and observing the system for a full start sequence.
Is the furnace power switch on?
The furnace usually has a service switch that looks like a common wall switch near the unit. Contractors and homeowners sometimes turn this OFF during service and forget to switch it back on. Ensure that switch is in the ON position and that the furnace control board has power.
If the switch was OFF, turning it ON will often let the furnace run. If the switch is ON but the unit still has no power, check the breaker or fuse next. Never operate the furnace if you see burned wiring or smell burning; cut power and call a technician.
Have you checked circuit breakers and fuses?
Inspect the main breaker panel for a breaker labeled furnace, HVAC, or heater. Reset a tripped breaker by switching it fully OFF then ON. For panels with labeled fuses, a blown fuse will prevent the control board from powering up. Replace fuses with the same type and rating only.
If a breaker or fuse trips again immediately, stop resetting it. Recurrent trips point to a motor fault, short, or overloaded circuit. Call a licensed electrician and HVAC technician to diagnose the electrical issue safely.
Is the pilot lit or ignitor clicking?
Older systems use a standing pilot light while modern furnaces use an electronic ignitor. If you hear repeated clicking but no flame appears, the ignitor may be failing. A worn ignitor or a dirty flame sensor will prevent the furnace from lighting. Do not try to adjust the gas valve; if you ever smell gas, evacuate and call emergency services instead of testing the unit.
Document any clicking, the number of attempts, and how the system responds. This information helps the technician find a faulty ignitor or control module more quickly.
Could a blocked condensate drain stop startup?
High-efficiency furnaces condense water and drain it away. A clogged condensate line or a tripped float switch in the secondary pan will keep the unit from running. Look for water or moisture around the furnace and check the secondary pan for standing water. Clearing the visible clog or replacing a drain trap can restore operation in some cases.
Do not bypass any safety switch. If clearing visible debris does not help, call a technician. A professional can inspect the condensate pump, trap, and float switch to ensure safe, lasting repair. (ASHRAE Technical Resources)
Airflow and Filters: what to inspect
Airflow problems are a top cause of furnace shutdowns and poor heating. Restricted airflow forces limit switches to open to protect the heat exchanger. A very dirty filter reduces airflow and makes the furnace overheat. Check the filter and replace disposable ones. Clean reusable filters according to the manufacturer's instructions. Note the filter size and rating before replacement.
Also inspect supply registers and return grilles. Closed or blocked registers, furniture in front of returns, and dirty ductwork all reduce airflow. Even with a clean filter, a collapsed or clogged return duct can create weak flow and uneven heat. If you see many vents with weak flow, document which rooms are worst for the technician.
When did you last replace the air filter?
A filter left in place for months can become nearly airtight. Replace disposable fiberglass or pleated filters on the recommended schedule. High-MERV filters can reduce airflow if the system is not designed for them. Use the correct filter type and check pressure drop if you suspect restriction. Regular filter changes reduce wear and let the furnace run normally.
If you remove the filter to test airflow, do not run the furnace long without a filter. Dust and debris can damage the blower and heat exchanger. If you find unusually heavy dust after a single season, schedule duct cleaning and a technician inspection.
Are vents and registers open?
Homeowners sometimes close registers to control temperatures or for cleaning. Closed supply registers or blocked returns can force the furnace to overheat and trigger safety limits. Walk the house before troubleshooting and open all registers. Remove grilles and clean them if they are obstructed by pet hair or dust.
Ensure the return grilles are clear. A blocked return location near the furnace is a common cause of limit trips. Reposition furniture and vacuum returns to restore airflow and prevent repeated shutdowns.
Can a clogged return duct cause no heat?
A compromised return duct will cut airflow even when filters and registers are clean. Signs include weak airflow at many registers, uneven heating, and frequent limit trips. Ducts can collapse, separate, or fill with insulation or debris. A professional assessment may reveal leaks, sagging, or a need for duct cleaning.
Duct repair often requires access in attics, crawl spaces, or basements. Have a technician evaluate balance, static pressure, and duct condition. Correcting return problems restores comfort and protects the furnace from overheating.
Thermostat and controls: what to check?
Thermostats fully control the heat call. Modern thermostats add convenience but also more points of failure. Check wiring and power first. A loose wire at the thermostat or control board can stop the heat call. Confirm the thermostat shows normal status and that it can call heat manually. If the thermostat reboots or shows error messages, write down codes and the model number for the technician.
Smart thermostats may rely on a C-wire for steady power. Without it they use batteries or power-stealing methods that can fail. If you suspect thermostat faults, switch to a simple programmable or manual thermostat temporarily to confirm whether the furnace responds to a basic call for heat.
How do smart thermostats affect startup?
Smart thermostats often need a common wire (C-wire) for continuous power. If the C-wire is missing, the device may attempt to steal power from the control circuit and behave erratically. Power issues can cause the thermostat to reboot or fail to send a heat signal. If the thermostat loses power, replace batteries or connect a C-wire adapter.
When in doubt, put the thermostat into manual heat and raise the setpoint. If the furnace still does not respond, the problem likely lies beyond the thermostat.
Does the thermostat show error codes?
Many modern thermostats display error codes when wiring or sensors fail. Write down any code and the thermostat model. This information shortens diagnostic time for an HVAC technician. Some codes point to sensor failures, wiring faults, or power losses.
If you see codes, do not guess at repairs. Share the exact code and the unit model when scheduling service so the technician brings the right tools and replacement parts, if needed.
Can WiFi issues stop heat calls?
Cloud outages or router problems can affect remote features of smart thermostats but they rarely stop local control. Manual control should still work even during an outage. Test by raising the indoor setpoint and checking if the furnace starts. If local control fails, the thermostat may have lost power or have internal faults, requiring repair or replacement.
If remote control is essential for your household, consider a thermostat that supports both local and cloud control, and keep a simple backup thermostat available for basic control during network outages.
Safety and electrical causes?
Electrical faults and safety interlocks protect the home but can also keep a furnace from starting. Visual inspection may reveal tripped breakers, blown fuses, or shut service switches. Smell for burning or look for scorch marks and melted insulation. If you detect these signs, cut power and call a professional. Never touch wiring or control boards without training.
Safety devices include limit switches, rollout switches, door interlocks, and float switches. These will stop operation when they detect a fault. Finding which device tripped is usually a technician task. Still, checking visible wiring, the service switch, and the breaker are useful first steps you can do safely.
Could a tripped breaker be the problem?
A tripped breaker is an easy-to-fix cause of total power loss. Reset it once by switching it fully off then on. If the breaker trips again quickly, do not keep resetting. Persistent trips usually point to a motor fault, shorted wiring, or an overloaded circuit. An electrician and HVAC tech should investigate.
Document the breaker label and any noises before or after the trip. This helps the technician identify whether the blower motor, control board, or another component caused the fault.
Is the service switch or emergency switch off?
Some furnaces include a wall-mounted service or emergency switch that looks like a light switch. Confirm that switch and the unit-mounted switch are ON. Ask household members if they switched the unit off during cleaning or testing. If someone turned the switch off, simply turning it on again may restore operation.
If the switch is ON but the unit still shows no power, proceed to the breaker and fuse checks. If you discover an unexpected off switch, note its location for future reference.
Can a blown fuse stop the furnace?
Older systems use fuses in the control circuit rather than breakers. A blown fuse prevents the control board from powering up. Replacing a fuse is straightforward if you know the correct replacement type and rating. However, repeated blown fuses indicate a deeper electrical problem that requires a technician to trace the cause.
If you replace a fuse and it blows immediately, stop and call for service. That behavior often signals a short or failed component that could be unsafe to operate.
Fuel and combustion issues to inspect?
Gas and combustion components are high risk and generally require a technician. Still, you can check a few safe items to collect useful information for the pro. Confirm the gas supply is on at the house valve and note whether other gas appliances work. If multiple appliances fail, the gas supply may be off or there may be an issue at the meter.
Never attempt to adjust gas valves, burners, or the gas control. If you smell gas, evacuate immediately and call emergency services. Combustion problems can produce carbon monoxide. If you suspect combustion issues, stop using the furnace and schedule immediate service.
Is the gas supply turned on at the valve?
Locate the gas shutoff near the furnace. The valve is ON when the handle is parallel to the pipe. If it is OFF, do not attempt to light the unit. Confirm no gas odor is present before turning the valve on. If you find the valve off and you did not turn it off, ask household members if work was done recently on the line.
If other gas appliances also fail, report that when you call the gas utility or a technician. They will check the meter and the home supply for interruptions.
Could a clogged burner or dirty flame sensor block ignition?
Burners and flame sensors accumulate residue over time. A dirty sensor can fail to detect flame and will shut the gas valve after ignition. Cleaning the flame sensor often restores normal operation. This task requires turning off power and working near gas, so many homeowners prefer a technician to do it.
If the burner ports are clogged or the flame is irregular, a pro should clean and adjust the burners. Proper combustion is essential for safety and efficiency.
When is it time to call a pro?
Call a licensed technician immediately if you smell gas, hear persistent ignition failures, detect carbon monoxide alarms, or cannot restore power after basic checks. Professionals have the tools to test combustion, measure CO, and safely handle electrical and gas components. Use credentials and written estimates when choosing service.
For non-urgent faults, schedule service in the shoulder season to avoid high emergency fees. Keep service records to help a technician diagnose recurring problems. If repairs exceed half the cost of replacement and the furnace is older than 15 years, replacement may be the better option for safety and efficiency.
What repair vs replacement rules apply by age?
If repair costs exceed half the price of a new system and the furnace is more than about 15 years old, replacement often makes more sense. Older furnaces are more likely to have heat exchanger fatigue and repeated failures. A replacement can lower energy bills and reduce safety risks tied to old equipment.
Talk to the technician about long-term costs, expected life, and available warranties. A clear, itemized estimate will help you compare options.
How much will a typical service call cost?
Diagnostic visits commonly range from $75 to $200, depending on your region and the season. Parts and labor add to the total. Ask for an itemized written estimate before work begins. For major repairs, consider getting two quotes to compare parts, labor, and warranties.
Emergency or after-hours calls often add 25–100 percent to standard fees. A pre-season tune-up helps avoid emergency repairs during cold snaps.
Are emergency or off season fees common?
Yes. Technicians charge more for nights, weekends, holidays, and emergency dispatches. These surcharges compensate for travel and prioritization. Scheduling routine maintenance before winter lowers the risk of emergency breakdowns and high fees.
If possible, arrange service during regular hours. Keep a list of licensed contractors and ask about emergency policies and hourly rates.
Start with safe checks: thermostat mode, fresh batteries, power switch, breaker, filter, and condensate. Avoid working on gas lines, burners, or complex electrical faults yourself. Choose a licensed, certified technician when problems persist or when you suspect combustion issues.
Las Vegas area homeowners needing fast, safe heating help can call The Cooling Company at 17029308411 for same-day diagnostics and repairs. The Cooling Company serves Las Vegas, Henderson, and North Las Vegas with NATE-certified techs and written estimates. If you live elsewhere, ask for NATE-certified technicians and request itemized repair quotes, then consider contacting The Cooling Company if you travel to our service area.
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About The Cooling Company
The Cooling Company has been serving the Las Vegas valley with professional HVAC services for over a decade. Our team of licensed, NATE-certified technicians specializes in air conditioning repair, heating system maintenance, and complete HVAC installations. We're committed to providing honest, reliable service with upfront pricing and a 100% satisfaction guarantee on all work performed.
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References
- U.S. Department of Energy (Energy.gov) (accessed 2026-01-02)
- U.S. Environmental Protection Agency (EPA) (accessed 2026-01-02)
- ASHRAE (Standards and guidance) (accessed 2026-01-02)
- ENERGY STAR (Heating & cooling) (accessed 2026-01-02)