When a Reznor propane heater stops working, most people assume the worst: bad gas valve, fried control board, time for a new unit.
In reality, the majority of heater problems I see are simple issues with simple fixes—dirty sensors, airflow problems, loose connections, or blocked venting.
This guide is your first-response troubleshooting manual. Before you call for service or start ordering parts, walk through these common problems, symptoms, and quick checks. You’ll either fix the issue outright or know exactly when it’s time to call a pro.
Reznor UDX 60,000 BTU Propane Unit Heater
🧯 Safety First (Always Comes First)
Before troubleshooting:
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Turn OFF power at the disconnect
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Shut OFF propane if opening gas components
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Let the heater cool
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Never bypass safety switches
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If you smell propane or exhaust gases—stop immediately and ventilate
Troubleshooting is maintenance, not risk-taking.
🔌 Problem #1: Heater Won’t Turn On at All
🔍 Common Symptoms
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No fan
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No ignition attempt
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No lights or sounds
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Thermostat calling for heat but nothing happens
🧠 Likely Causes
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No power to unit
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Tripped breaker or blown fuse
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Faulty thermostat or wiring
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Open safety switch
✅ Quick Fix Checklist
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Check breaker and disconnect
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Verify thermostat settings and batteries
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Inspect wiring connections at the unit
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Look for tripped rollout or limit switches
Tony’s take:
If there’s no power, the heater can’t even try to fail. Start here every time.
🔥 Problem #2: Heater Tries to Start but Won’t Ignite
🔍 Common Symptoms
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Fan runs, but no flame
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Clicking sounds with no ignition
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Repeated ignition attempts, then lockout
🧠 Likely Causes
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Dirty igniter
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Dirty or blocked burner
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No propane flow
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Faulty gas valve or control signal
✅ Quick Fix Checklist
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Confirm propane supply is ON
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Clean burner assembly and orifices
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Inspect igniter for cracks or carbon buildup
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Reset the unit and retry
🔗 Furnace ignition troubleshooting (DOE):
https://www.energy.gov/energysaver/furnaces-and-boilers
🔄 Problem #3: Heater Lights, Then Shuts Off Quickly
🔍 Common Symptoms
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Flame appears briefly
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Unit shuts down within seconds
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Repeats cycle or locks out
🧠 Likely Causes
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Dirty flame sensor (most common)
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Poor ground
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Weak flame signal
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Combustion air restriction
✅ Quick Fix Checklist
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Remove and clean flame sensor with fine emery cloth
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Check grounding connections
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Inspect combustion air openings
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Observe flame quality (should be steady blue)
Tony’s take:
If your heater lights and quits, clean the flame sensor before blaming electronics.
🌬️ Problem #4: Fan Runs, But No Heat
🔍 Common Symptoms
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Blower runs normally
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No flame or heat output
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Cold air movement
🧠 Likely Causes
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Gas valve not opening
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Pressure switch issue
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Venting or combustion air problem
✅ Quick Fix Checklist
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Check vent pipe for blockage
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Inspect pressure switch tubing
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Confirm propane supply pressure
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Look for error codes (if equipped)
🌡️ Problem #5: Heater Cycles On and Off Too Often
🔍 Common Symptoms
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Short run times
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Frequent starts and stops
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Inconsistent shop temperature
🧠 Likely Causes
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Overheating due to poor airflow
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Dirty blower or fan
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Blocked discharge louvers
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Incorrect thermostat placement
✅ Quick Fix Checklist
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Clean blower wheel and fan
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Verify clear airflow paths
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Check temperature rise
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Relocate thermostat if near drafts or heat sources
Short cycling kills efficiency and parts—don’t ignore it.
🔊 Problem #6: Unusual Noises (Rattling, Squealing, Humming)
🔍 Common Symptoms
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Rattling during startup
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Squealing or grinding
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Loud vibration
🧠 Likely Causes
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Loose mounting hardware
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Dirty or unbalanced blower
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Dry or failing motor bearings
✅ Quick Fix Checklist
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Tighten all accessible fasteners
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Clean blower wheel
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Lubricate motor (if oilable)
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Inspect motor mounts
🔗 Electric motor maintenance basics:
https://www.energy.gov/eere/buildings/electric-motors
🌫️ Problem #7: Yellow or Lazy Flames
🔍 Common Symptoms
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Yellow flame tips
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Flickering or rolling flame
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Soot accumulation
🧠 Likely Causes
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Dirty burners
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Restricted combustion air
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Blocked venting
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Improper gas/air mix
✅ Quick Fix Checklist
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Clean burner tubes thoroughly
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Clear combustion air openings
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Inspect vent termination outside
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Remove nearby obstructions
🔗 Propane flame characteristics:
https://propane.com/propane-safety-in-your-home/
🚨 Problem #8: Heater Shuts Down Randomly (Safety Trips)
🔍 Common Symptoms
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Heater runs fine, then shuts off
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Requires manual reset
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Happens more in cold or windy weather
🧠 Likely Causes
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Venting pressure issues
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Wind affecting termination
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Overheating
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Weak pressure switch
✅ Quick Fix Checklist
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Inspect vent slope and connections
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Check exterior termination location
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Clean blower and airflow path
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Verify heater clearances
Random shutdowns usually aren’t random—something is borderline.
🧪 Problem #9: Strong Smells or Eye Irritation
🔍 Common Symptoms
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Sharp odor during operation
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Headaches or irritation
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CO detector alerts
🧠 Likely Causes
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Incomplete combustion
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Exhaust leakage
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Cracked heat exchanger
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Vent failure
✅ What to Do Immediately
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Shut the heater OFF
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Ventilate the space
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Do NOT restart until inspected
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Call a professional immediately
🔗 Carbon monoxide safety:
https://www.cpsc.gov/Safety-Education/Safety-Education-Centers/Carbon-Monoxide-Information-Center
🧠 Error Codes & Control Board Indicators
Many newer Reznor units include diagnostic LEDs.
Best practices:
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Count flashes carefully
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Reference the unit’s manual
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Don’t guess—codes are clues
🔗 Reznor manuals & diagnostics:
https://www.reznorhvac.com
🛑 When DIY Troubleshooting Stops
Call a licensed technician if you encounter:
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Gas pressure issues
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Repeated lockouts
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CO detector alarms
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Heat exchanger damage
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Electrical control failures
DIY maintenance saves money. DIY gas diagnostics can cost lives.
🏁 Final Word from Tony
Reznor heaters are tough—but they still need attention.
Most problems come down to:
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Dirty parts
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Restricted airflow
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Loose connections
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Ignored maintenance
If you troubleshoot smart, clean what’s dirty, and listen to what the heater is telling you, you’ll fix most issues before they become expensive ones.
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In the next topic we will know more about: Deep Cleaning Your Heat Exchanger: Why It Matters & How to Do It Right
