If you own a Mr Heater Big Maxx garage or shop heater, you know how valuable it is during cold months. This powerful unit keeps your workspace warm and comfortable, letting you focus on work instead of shivering. But like any gas-powered appliance, problems can arise. When your Big Maxx won’t start, makes strange noises, or heats poorly, it’s more than an annoyance—it can halt your work and even create safety concerns.
This guide is written for anyone who wants to troubleshoot their Mr Heater Big Maxx. Maybe you’re a homeowner trying to fix your garage heater, or a small business owner keeping the workshop running. Either way, you’ll find practical, step-by-step help. We’ll cover common problems, what causes them, and how to solve them safely. You’ll also learn two key things most people miss: how small details like venting or gas pressure can impact performance, and why regular maintenance is just as important as quick fixes.
Let’s dive into making your Big Maxx reliable, efficient, and safe again.
Understanding The Mr Heater Big Maxx
Before troubleshooting, it helps to know the basics of how the Big Maxx works. This knowledge will make it easier to spot what’s wrong and avoid unnecessary repairs.
Main Features
- Forced air gas heater: Uses natural gas or propane to produce heat.
- Electronic ignition: Most models use an automatic spark to light the burner.
- Fan-forced: A built-in fan circulates warm air.
- Thermostat control: Maintains your set temperature.
- Safety shutoff: Turns the unit off if something’s wrong.
Key Components
| Component | Function |
|---|---|
| Ignitor | Lights the gas when the unit starts |
| Gas valve | Controls flow of gas to the burner |
| Flame sensor | Detects if the burner is lit |
| Thermostat | Signals heater to turn on/off as needed |
| Fan motor | Pushes heated air into the room |
| Vent/exhaust | Releases combustion gases outside |
Knowing these components helps you understand where things can go wrong.
Safety First: What To Do Before Troubleshooting
Whenever you work with gas appliances, safety comes first. Gas leaks, electric shock, and fire hazards are real risks. Here’s what to do before you start:
- Turn off power: Unplug the heater or shut off the breaker.
- Shut off gas: Close the main gas valve supplying the heater.
- Let the unit cool: Wait at least 30 minutes after use.
- Read the manual: Check your model’s guide for safety notes.
- Ventilate: Open doors/windows if you smell gas.
If you ever smell strong gas, leave the area immediately and call your gas provider. Never try to fix a suspected leak yourself.
Common Mr Heater Big Maxx Problems And How To Fix Them
Even reliable heaters can have issues. Here are the most frequent Big Maxx problems, their likely causes, and practical solutions.
1. Heater Won’t Start
This is the most common issue. The heater does nothing when you set the thermostat.
Possible Causes:
- No power to unit
- Thermostat set too low or faulty
- Tripped safety switch
- Bad ignitor
- Gas supply problem
How to Fix:
- Check power: Make sure the unit is plugged in and the breaker isn’t tripped.
- Thermostat: Set above room temperature. If still nothing, try bypassing (connect wires together briefly). If heater starts, replace thermostat.
- Safety switches: Some units have a reset button—press it.
- Ignitor: Listen for clicking. No click means faulty ignitor or control board.
- Gas supply: Ensure main valve is open. Try a different gas appliance—if it doesn’t work, call your gas provider.
Non-obvious insight: Many users overlook loose thermostat wiring. Check for any disconnected or loose wires at the thermostat and heater terminals.
2. Heater Clicks But Won’t Light
You hear clicking (ignitor firing), but there’s no flame.
Likely Causes:
- Gas valve off or faulty
- Air in the gas line (common after new install)
- Dirty or misaligned ignitor
- Blocked burner
How to Fix:
- Gas valve: Confirm it’s in the ON position.
- Purge air: Turn heater on and off a few times to push air out. Open a window for ventilation.
- Ignitor: Clean with fine sandpaper. Realign so spark touches burner.
- Burner: Remove and clean with compressed air.
Pro tip: If you just installed or reconnected gas, it may take several tries to purge air from the line. Patience helps.
3. Heater Starts, Then Shuts Off
The heater fires up but stops after a few seconds or minutes.
Possible Causes:
- Faulty flame sensor
- Blocked vent or exhaust
- Overheating (high-limit switch tripped)
- Dirty air filter
How to Fix:
- Flame sensor: Clean gently with steel wool. A dirty sensor can’t “see” the flame, so the unit shuts off for safety.
- Vent: Check outside vent for birds’ nests, snow, or debris.
- High-limit switch: Check for blocked airflow (dirty filter, closed vents). Reset the switch if your model has one.
- Filter: Clean or replace as recommended.
Non-obvious insight: A blocked exhaust vent can cause the heater to cycle on and off. Even a small obstruction outside can make a big difference.
4. Heater Runs, But No Heat
Fan works, but the air feels cold.
Possible Causes:
- Gas supply low or off
- Burner not lighting
- Faulty gas valve
- Thermostat set to “fan” instead of “heat”
How to Fix:
- Gas supply: Confirm supply and pressure.
- Burner: Listen for ignition and check for visible flame through the sight glass.
- Gas valve: If everything else checks out, you may need a new valve.
- Thermostat mode: Ensure it’s set to “heat.”
5. Heater Makes Strange Noises
You hear banging, rattling, or whistling.
Possible Causes:
- Loose panels or screws
- Dirty fan blades
- Expanding/contracting metal
- Gas pressure issues (whistling)
How to Fix:
- Tighten: Check all access panels and screws.
- Clean: Remove dust from fan with a vacuum or soft brush.
- Gas pressure: Have a professional check pressure if you hear persistent whistling.
- Expansion noise: Some popping is normal as metal heats/cools.
6. Fan Not Working
Heater fires, but no air blows.
Possible Causes:
- Bad fan motor
- Faulty fan relay
- Blocked airflow
- Broken fan belt (if equipped)
How to Fix:
- Motor: Test with a multimeter or have an electrician check.
- Relay: Listen for a click when the heater starts. No click may mean a bad relay.
- Airflow: Check for obstructions at intake and output.
- Belt: Replace if worn or broken.
Error Codes And What They Mean
Many newer Big Maxx heaters have LED error codes. These codes help you identify problems quickly. Here’s a quick reference:
| LED Code | Meaning | What to Check |
|---|---|---|
| Continuous Flash | Normal operation | No action needed |
| 1 Flash | Ignition failure | Gas supply, ignitor, flame sensor |
| 2 Flashes | Flame detected with gas valve off | Flame sensor, control board |
| 3 Flashes | Pressure switch error | Vent blockage, switch wiring |
| 4 Flashes | High limit (overheat) | Dirty filter, blocked vents |
Always check your model’s manual for exact codes.
Step-by-step Troubleshooting For Beginners
If you’re not sure where to start, follow this order. It helps you avoid missing simple fixes.
Step 1: Check Power And Thermostat
- Confirm the unit is plugged in.
- Breaker should be ON.
- Thermostat set higher than room temperature.
Step 2: Inspect Gas Supply
- Gas valve should be open.
- If using propane, check the tank level.
- Try another gas appliance (like a stove) to test supply.
Step 3: Look For Error Codes
- Open the access panel.
- Watch the control board’s LED for flashes.
- Match the flashes to the table above.
Step 4: Examine The Ignitor And Flame Sensor
- Remove the access panel.
- Clean the ignitor tip and flame sensor with steel wool.
- Reinstall and try starting the heater.
Step 5: Check The Vent And Airflow
- Inspect outdoor vent for blockages.
- Clean or replace air filter.
- Make sure nothing is blocking the intake or output.
Step 6: Reset Safety Switches
- Some models have a reset button near the burner.
- Press and hold for 5 seconds.
Step 7: Test The Fan
- Turn on the heater and listen for the fan.
- If silent, check for power at the fan motor.
- Replace fan relay if needed.
Pro tip: Take photos before disconnecting any wires. This helps you reconnect them correctly.
When To Call A Professional
Not every problem can (or should) be fixed by the owner. Call a licensed technician if:
- You smell gas and shutting off the valve doesn’t help.
- The control board, gas valve, or pressure switch needs replacing.
- You’re unsure about any wiring.
- The heater needs a new vent or gas line.
- There’s water or rust inside the unit.
Trying to fix these without experience can be dangerous and may void your warranty.
Preventive Maintenance For Mr Heater Big Maxx
Regular care prevents most problems and keeps your heater running smoothly for years.
What To Do Annually
- Clean the flame sensor and ignitor: Build-up causes most ignition issues.
- Check and clean air filter: Blocked filters cause overheating.
- Inspect vent pipe: Remove any blockages.
- Tighten all screws and panels: Reduces noise and vibration.
- Test thermostat: Replace if readings are wrong.
- Lubricate fan motor (if required): See your manual.
- Check for rust or corrosion: Address any leaks immediately.
Every 3-6 Months
- Wipe down exterior.
- Listen for new noises.
- Check for error codes.
By doing simple checks, you avoid expensive repairs later.
Common Installation Mistakes That Cause Problems
Sometimes, the issue isn’t the heater—it’s how it was installed. Two common mistakes:
- Improper venting: Big Maxx needs the right size and type of vent pipe. Too small, long, or full of bends means poor combustion, frequent cycling, or dangerous fumes. Always follow the manual’s venting diagram.
- Wrong gas pressure: Both natural gas and propane models need precise pressure. Too high or low, and you’ll get weak heat, error codes, or a failed ignitor. Pressure should be checked with a manometer during install.
If you’re unsure, have a pro double-check your setup.
Spare Parts: What Fails Most Often
Some parts wear out faster than others. Here’s what you might need to replace over the years:
- Flame sensor
- Ignitor
- Gas valve
- Fan relay
- Thermostat
These parts are widely available online and from Mr Heater dealers. Always use genuine replacements to avoid further issues.
Comparing Mr Heater Big Maxx To Similar Units
If you’re wondering how the Big Maxx compares to other garage heaters, here’s a quick look:
| Feature | Mr Heater Big Maxx | Modine Hot Dawg | Reznor UDAP |
|---|---|---|---|
| BTU Range | 50,000–80,000 | 30,000–75,000 | 30,000–125,000 |
| Ignition | Electronic | Electronic | Electronic |
| Fuel | Natural Gas/Propane | Natural Gas/Propane | Natural Gas/Propane |
| Warranty | 3 years | 10 years (heat exchanger) | 10 years (heat exchanger) |
| Price (approx.) | $600–$900 | $900–$1,200 | $1,000–$1,500 |
The Big Maxx is popular for its balance of price, features, and reliability. But if you want a longer warranty or larger capacity, other brands may be worth a look.
Real-world Examples
Example 1: John’s Big Maxx wouldn’t start after a power outage. He found the breaker had tripped—flipping it back solved the problem.
Example 2: Maria’s heater kept shutting off. She discovered a bird’s nest in the vent pipe. Removing it fixed the cycling issue.
Example 3: Dave’s unit ran but blew cold air. His gas supply was off after the propane tank was changed. Opening the valve restored heat.
These examples show that most issues are simple once you know where to look.
Resources For Further Help
- Official Mr Heater website: User manuals, troubleshooting guides, and parts diagrams.
- YouTube: Search “Mr Heater Big Maxx troubleshooting” for video guides.
- Local HVAC professionals: Certified help for major repairs.
For more technical details, see the Mr Heater official site.
Frequently Asked Questions
Why Does My Mr Heater Big Maxx Keep Shutting Off?
Most often, this is due to a dirty flame sensor, blocked vent, or overheating from poor airflow. Clean the sensor and check the vent. Also, make sure the filter isn’t clogged.
How Do I Reset My Big Maxx Heater?
Many models have a small reset button near the burner or control board. Press and hold for 5 seconds. If it keeps tripping, find and fix the underlying problem before resetting again.
Can I Use Propane With My Big Maxx If It Was Set Up For Natural Gas?
Some models are convertible, but you need a conversion kit and must adjust the gas pressure. It’s best to have a professional do the conversion to avoid leaks or poor combustion.
What Should I Do If I Smell Gas?
Turn off the heater, shut the gas valve, ventilate the area, and leave the building immediately. Contact your gas provider or fire department. Never try to fix a leak yourself.
How Often Should I Clean Or Service My Big Maxx?
Clean the flame sensor and filter at least once a year. Full service (by a technician) is recommended every 2–3 years, or sooner if you use the heater heavily.
—
A well-maintained Mr Heater Big Maxx should give you years of reliable warmth. Remember: Most problems are simple, and a little regular care goes a long way. With the right troubleshooting steps, you can solve many issues yourself, but don’t hesitate to call a professional for gas or electrical repairs. Your safety—and comfort—come first.
