🔥 Heating System Failures
Why Your Heat Isn’t Working—and What to Check
🧠 Why Heating Systems Fail
Heating systems rely on fuel, airflow, combustion, and electrical controls to operate correctly.
Failures usually happen because of:
- Lack of maintenance
- Worn-out components
- Electrical problems
- Airflow restrictions
- Sensor faults or safety lockouts
🛠️ Understanding the symptoms can help you diagnose faster—and avoid costly breakdowns.
🚨 Common Heating System Failures
| Failure Type | Symptoms | Likely Cause |
|---|---|---|
| No Heat at All | Thermostat set correctly but no heat | Power issue, control board failure, blown fuse |
| Blower Running But No Heat | Fan moves air but it’s cold | Ignition failure, gas valve issue, flame sensor dirty |
| System Short Cycling | Turns on and off rapidly | Overheating, dirty filter, bad flame sensor |
| Furnace Won’t Ignite | Clicking sound, no flame | Bad ignitor, bad gas valve, pressure switch fault |
| Heat Pump Not Heating | Outdoor unit runs but blows cold air | Reversing valve stuck, low refrigerant, sensor failure |
| Boiler Not Heating | No hot water to radiators/baseboards | Circulator pump failure, low water pressure, bad thermostat |
| Strange Odors | Burnt smell or gas smell | Dust on heat exchanger (normal at startup) OR gas leak (danger!) |
| Water Leak (Boiler) | Puddles near boiler | Cracked heat exchanger, faulty relief valve, pipe leak |
🧰 Heating System Components That Commonly Fail
| Component | Function | Common Failure |
|---|---|---|
| Ignitor (Hot Surface or Spark) | Lights burner flame | Cracks over time, burns out |
| Flame Sensor | Proves burner is lit | Gets dirty, loses signal, causes lockout |
| Pressure Switch | Confirms safe draft/exhaust | Hoses clog, switch sticks |
| Limit Switch | Shuts off furnace if overheating | Can trip from dirty filters, closed vents |
| Control Board | Brain of system, routes power | Fails from moisture, shorts, surges |
| Thermocouple (Boilers) | Detects pilot flame | Wears out over years, can’t hold valve open |
| Circulator Pump (Boiler) | Moves water through pipes | Motor burnout, stuck impeller |
🛠️ Quick Troubleshooting Steps
| Step | Check This |
|---|---|
| Thermostat | Batteries, settings (heat mode, temp higher) |
| Filter | Dirty filters cause high limit trips |
| Breakers/Fuses | Reset if tripped; check disconnect switches |
| Furnace Panel Door | Door switches kill power if panel loose |
| Pressure Switch Tubing | Inspect for kinks & blockage |
| Outdoor Unit (Heat Pump) | Defrost mode working? Ice buildup? |
| Gas Valve (Furnace) | Confirm gas supply is open |
🧠 If the system goes into lockout (multiple failed tries), you’ll often need to manually reset it at the power source.
⚡ Electrical Failures vs. Mechanical Failures
| Type | Common Examples | Symptoms |
|---|---|---|
| Electrical | Bad board, dead capacitor, shorted relay | Dead system, erratic behavior |
| Mechanical | Stuck motor, cracked ignitor, worn inducer | Noises, hard start, shutdowns |
🔌 Always check voltage (24V and high voltage) if a system acts completely dead.
💧 Combustion Problems (Gas Systems)
| Combustion Issue | Symptoms | Safety Risk |
|---|---|---|
| Incomplete Combustion | Yellow flame, soot buildup | High carbon monoxide (CO) risk |
| Blocked Flue | Furnace shuts down or CO detector trips | Serious—must clear vent ASAP |
| Cracked Heat Exchanger | Strange smells, CO alarm, visible cracks | Very high safety hazard |
🛡️ CO alarms near furnaces and sleeping areas are critical for safety!
📉 Heating System Lifespan Estimates
| System Type | Average Lifespan | Notes |
|---|---|---|
| Gas Furnace | 15–20 years | Good maintenance extends life |
| Electric Furnace | 20–25 years | Fewer moving parts, longer life |
| Heat Pump | 10–15 years | Coastal climates wear them faster |
| Boilers (Water-Based) | 20–30 years | Cast iron lasts longer than steel |
🛠️ Systems past 15 years old may be more cost-effective to replace than repair.
✅ Preventing Heating Failures
| Preventive Step | Benefit |
|---|---|
| Annual Maintenance | Cleans burners, sensors, confirms safeties |
| Filter Changes (every 1–3 mo) | Keeps airflow strong, protects heat exchanger |
| Inspect Ignitors/Flame Sensors | Catch failing parts before winter |
| Check Gas Pressures (Pros) | Ensure combustion tuning and safety |
| Verify Defrost Cycles (Heat Pumps) | Prevents freeze-up in winter |
📘 Final Thoughts
Heating systems are complex machines with simple symptoms.
Whether it’s no ignition, short cycling, frozen coils, or no heat, starting with airflow, power, combustion, and controls will diagnose most issues.