As temperatures plummet and winter settles in, HVAC companies experience their busiest season of the year. Service calls spike dramatically, and technicians see the same recurring problems across residential and commercial properties.
Whether you’re considering furnace installation arvada co, or maintaining an existing system, understanding these common peak-season issues helps you prevent breakdowns when you need heating most.
This guide reveals the furnace problems HVAC professionals encounter most frequently during winter and what causes them.
The Dreaded No-Heat Emergency
Thermostat Malfunctions
One of the most common service calls involves furnaces that won’t turn on, and surprisingly, the furnace itself often isn’t the problem. HVAC technicians report that thermostat issues account for a significant portion of no-heat calls.
Dead batteries: Many thermostats rely on AA or AAA batteries that die without warning, shutting down the entire heating system.
Incorrect settings: Thermostats accidentally switched to “cool” mode or set to “fan only” rather than “auto” create the illusion of furnace failure.
Poor placement: Thermostats installed near drafty windows, direct sunlight, or heat-producing appliances give false temperature readings, causing improper cycling.
Wiring problems: Loose connections or corroded wires prevent thermostats from communicating with furnaces.
Tripped Breakers and Blown Fuses
Electrical issues rank among the top reasons furnaces stop working during peak season. When furnaces draw excessive power at startup or electrical components fail, circuit breakers trip or fuses blow as safety mechanisms.
HVAC companies frequently respond to panicked calls about non-functioning furnaces, only to discover a simple tripped breaker in the electrical panel. However, repeated breaker trips indicate deeper electrical problems requiring professional diagnosis.
Dirty Filter Disasters
The Number One Preventable Problem
Ask any HVAC technician about the most common issue they encounter, and they’ll immediately mention clogged air filters. During peak season, when furnaces run constantly, filters accumulate debris rapidly. Homeowners and business owners often neglect this simple maintenance task, leading to cascading problems.
Consequences of Neglected Filters
Reduced airflow: Clogged filters restrict air movement, forcing furnaces to work harder and run longer to achieve desired temperatures. This inefficiency dramatically increases energy bills.
Overheating and shutdowns: When airflow is severely restricted, heat exchangers overheat. Modern furnaces have safety switches that shut down the system before damage occurs, leaving you without heat.
Blower motor strain: Motors working against restricted airflow overheat and fail prematurely. Blower motor replacement is expensive compared to regular filter changes.
Poor indoor air quality: Saturated filters can’t capture additional particles, allowing dust, allergens, and contaminants to circulate throughout your property.
HVAC companies recommend checking filters monthly during peak season and replacing them when they appear gray or dirty, typically every 1-3 months depending on usage and filter type.
Ignition and Pilot Light Problems
Electronic Ignition Failures
Modern furnaces use electronic ignition systems rather than standing pilot lights. During peak season, these systems fail due to dirty flame sensors, faulty ignition modules, electrical surges, or cracked hot surface igniters.
Technicians report that flame sensor buildup is particularly common. The sensor rod develops a coating that prevents it from detecting flames, causing the furnace to shut down seconds after ignition as a safety precaution.
Pilot Light Issues in Older Systems
For properties with older furnaces still using standing pilot lights, common peak-season problems include pilot lights that won’t stay lit due to faulty thermocouples, dirty pilot assemblies, inadequate gas supply, or draft issues.
A thermocouple that’s worn or positioned incorrectly won’t generate enough voltage to keep the gas valve open, requiring professional adjustment or replacement.
Airflow and Distribution Problems
Uneven Heating Complaints
Peak season brings numerous service calls about rooms that are too hot or too cold despite the furnace running constantly. HVAC companies typically find these causes:
Closed or blocked vents: Furniture, curtains, or debris blocking supply or return vents disrupts airflow balance throughout the property.
Duct leaks: Gaps, holes, or disconnected ductwork allow heated air to escape into attics, crawl spaces, or walls before reaching intended spaces.
Improper damper settings: Zone dampers stuck in the wrong positions or manual dampers accidentally closed prevent proper air distribution.
Undersized ductwork: Original installations with inadequate duct sizing struggle to distribute heat effectively, especially noticeable during extreme cold when furnaces run continuously.
Blower Motor and Fan Issues
The blower assembly circulates heated air throughout your property. During peak time, when systems run constantly, HVAC technicians encounter blower motors that run continuously without stopping, make unusual noises like squealing or grinding, cycle on and off erratically, or fail to turn on at all.
Worn bearings, loose fan blades, capacitor failures, and accumulated debris on fan wheels are common culprits. These problems worsen rapidly under continuous peak-season operation.
Heat Exchanger Concerns
Cracks and Damage
The heat exchanger is your furnace’s most critical and expensive component. It separates combustion gases from breathable air while transferring heat. During peak season, HVAC companies discover heat exchanger problems that often went unnoticed during milder weather.
Causes of damage: Years of thermal expansion and contraction, corrosion from combustion byproducts, inadequate maintenance causing overheating, and manufacturing defects in some models.
Warning signs: Unusual smells like formaldehyde, visible soot or corrosion, yellow or flickering burner flames instead of steady blue, and excessive moisture around the furnace.
Cracked heat exchangers pose serious carbon monoxide risks. Responsible HVAC companies immediately shut down furnaces with confirmed cracks and recommend replacement, as heat exchanger replacement often costs nearly as much as a new furnace.
Gas Supply and Burner Issues
Dirty Burners
During combustion, burners can accumulate rust, dust, and carbon deposits. When furnaces operate heavily, dirty burners cause delayed ignition (creating small explosions at startup), yellow or orange flames instead of blue, sooty buildup around the furnace, and reduced heating efficiency.
Professional burner cleaning restores proper combustion and prevents more serious problems.
Gas Valve Problems
HVAC technicians encounter gas valves that stick partially closed or open, fail to open completely when called for heat, or leak gas, creating dangerous situations.
Gas valve issues require immediate professional attention and typically necessitate valve replacement rather than repair.
Condensate Drain Blockages
Especially Common in High-Efficiency Furnaces
High-efficiency furnaces produce condensation during operation. During peak season, condensate drain lines can freeze in cold weather, become clogged with algae or debris, disconnect due to improper installation, or develop clogs at drain traps.
When condensate can’t drain properly, safety switches shut down the furnace to prevent water damage. HVAC companies frequently respond to these calls during the coldest stretches of winter when furnaces produce maximum condensate.
Limit Switch Failures
Overheating Safety Devices
Limit switches protect furnaces from overheating by monitoring temperatures and shutting down systems when they exceed safe levels. During peak season, these switches can fail due to age and wear, inadequate airflow causing excessive cycling, electrical problems, or accumulated dust and debris.
A failed limit switch might cause the furnace to run continuously without cycling properly, shut down prematurely before reaching temperature, or fail to turn on the blower when it should.
Strange Noises and What They Mean
Peak Season Noise Complaints
As furnaces work overtime during winter, homeowners and facility managers notice sounds that weren’t apparent during lighter usage. HVAC technicians diagnose problems based on specific noises:
Banging or booming: Delayed ignition causes small gas buildups that ignite suddenly, or ductwork expanding and contracting with temperature changes.
Squealing or screeching: Blower motor bearings failing or belts slipping or wearing out.
Rattling: Loose panels or components, debris in blower assembly, or failing motors.
Humming: Electrical issues or transformer problems.
While some noises are merely annoying, others indicate serious problems requiring immediate attention.
Carbon Monoxide Concerns
The Silent Winter Danger
During peak season, when furnaces run constantly, and homes are sealed tight against cold weather, carbon monoxide risks increase. HVAC companies take CO concerns extremely seriously.
Common causes: Cracked heat exchangers, blocked or damaged flue pipes, inadequate combustion air supply, or backdrafting from improper venting.
Critical symptoms: Frequent headaches when indoors, nausea or dizziness, flu-like symptoms affecting multiple household members, or carbon monoxide detector alarms.
Professional HVAC companies carry CO testing equipment and immediately investigate any suspected carbon monoxide issues, shutting down furnaces if necessary until repairs ensure safe operation.
Age-Related Failures
When Furnaces Hit Their Limits
Peak season’s continuous operation stress reveals age-related problems in older systems. HVAC companies report that furnaces over 15-20 years old experience more frequent breakdowns, require increasingly expensive repairs, operate less efficiently, and have difficulty maintaining consistent temperatures.
Many emergency service calls during peak season involve older furnaces finally reaching their end of life. The stress of continuous winter operation becomes the final straw for systems already compromised by years of wear.
Prevention Strategies
What HVAC Companies Recommend
Based on the issues they encounter most frequently, HVAC professionals emphasize these preventive measures:
Pre-season maintenance: Schedule professional inspections and tune-ups before peak season begins, ideally in early fall.
Regular filter changes: Check monthly, replace as needed, the single most important maintenance task.
Clear surroundings: Keep furnace areas clear of storage items, ensure proper ventilation, and maintain clearance requirements.
Monitor performance: Pay attention to unusual sounds, smells, or performance changes and address them promptly.
Install CO detectors: Place carbon monoxide detectors on every level and test them regularly.
Upgrade aging systems: Replace furnaces approaching 15-20 years old before they fail during peak season.
When to Call Professionals
Don’t Wait for Complete Failure
HVAC companies encourage property owners to call at the first signs of problems rather than waiting for complete breakdowns. Early intervention prevents minor issues from escalating into expensive emergency repairs.
Call immediately for any gas odors, carbon monoxide detector alarms, no heat during extreme cold, strange noises or burning smells, or visible flames, smoke, or sparks.
For less urgent concerns like reduced efficiency, minor noises, or uneven heating, schedule service promptly rather than hoping problems resolve themselves.
The Bottom Line
Peak season reveals furnace weaknesses that moderate weather masks. HVAC companies respond to the same common issues repeatedly, most of which are preventable through regular maintenance. Understanding these problems helps property owners take preventive action and recognize when professional help is necessary.
The key insight from HVAC professionals is simple: furnaces rarely fail randomly. Most peak-season breakdowns result from deferred maintenance, age-related wear, or problems that developed gradually. By staying vigilant, maintaining systems properly, and addressing small issues before they escalate, you can avoid becoming another peak-season emergency service call when you need heat most.
