Troubleshooting Mr. Heater Big Maxx 4 Flashes [Easy Fixes]

Mr. Heater Big Maxx 4 flashes on the control board as an error indication of an opened high limit switch or flame rollout switch in the unit. The error is typically derived from the exceeding temperature in the system, which triggers the high limit switch to protect the heater from overheating dangers.

When the error occurs, simply turn off the unit and let it cool down. After this self-diagnostic period, the system will get back to normal operation after cooling down.

If not, you will need to have a detailed inspection. The root causes of a continuous high limit switch tripping in a Mr. Heater Big Maxx may include:

  • Blocked ventilation
  • Malfunctioning control board
  • Non-operational blower motor
  • Gas pressure issue
  • Or the defective switch itself. 

Keep reading to get the easiest solution ideas for this issue from my hands-on experience operating Mr. Heater Big Maxx.

mr. heater big maxx 4 flashes

Table of Contents

Possible Reasons & Solutions For 4 Flashes On The Mr. Heater Big Maxx [Quick Overview]

Before getting into the details, let’s have a short glimpse at the quick table below, which highlights all the possible reasons for causing your Mr. Heater’s Big Maxx high limit switch to open and lead to 4 flashes in the status light.

Here is a quick overview of the needed steps to deal with the issues as well:

Probable Reasons Recommended Fix 
Blocked venting Inspect the vents for any blockages and clean them. 
Malfunctioning blower motor Check and ensure the neutral wire of the fan is properly connected with the supply voltage neutral.
Low manifold gas pressure Measure the gas pressure of your heater and adjust it to the specific level. 
Malfunctioning control board Examine the voltage in the ACC terminal of the board for 120 volts. If not, the board is bad and needs quick servicing.
Defective high-limit switch Replace the bad switch with the help of a professional. 

Troubleshooting Mr Heater Big Maxx 4 Flashes [Easy Solutions]

After the quick overview, you can now understand that the 4 flashes on the Mr. Heater control board are a clear signal of an overheated unit. Most of the users find this code very easy to deal with, while others need professional assistance.

So before heading to any professional repair, here are the DIY troubleshooting methods you can apply to deal with issues when your MR heater Big Maxx high limit or rollout switch opens, leading to an LED 4 flash code.

1. Power Cycle Your Garage Heater

A high-limit switch on the heater is a safety cut-off device that triggers an extreme ambient temperature. That means when the air inside the system gets too hot or the temperature exceeds the preset limit, it is obvious the limit switch will open and cut off the power to the unit.

So as for the first method, we need to cool down the heater to minimize the inside temperature. For instance, we can simply start by power-cycling the unit. This can help clear any faults or glitches as well.

To reset your unit:

Step #1: Turn off the power supply to the heater. For instance, unplug it from the power connection or simply flip the circuit breaker to the Off position.

Step #2: Then turn the gas valve to the closed/off position.

Step #3: Wait 5-10 minutes to allow the heater to fully power down and let the gas dissipate properly to cool off the components. This cooling-off period is important – don’t rush it.

Step #4: After that time, turn the gas supply back on. Flip the circuit breaker to the On position and plug the unit back in.

Step #5: Check the control board if the LED is flashing. Hopefully not! 

control board of mr. heater big maxx

2. Reset The High Limit Switch

The high-limit switch or flame roll-out switch of any gas furnace is resettable by equipping a reset button in the middle of the switch assembly.

As with the unit overheating, the switch trips and cuts off the power to the unit. When the heater cools down, the switch closes and turns back to its normal operation.

If there are still 4 flashing codes on your Mr. Heater Big Maxx even after power cycling, you can manually try to reset the switch. It will reset the complete heater system and set it to the factory default setting.

Here is how you will reset your Mr heater Big Maxx heater through a high-limit switch:

Step #1: Safety first! Turn off the power supply to your garage heater. Turn it off from the control panel and unplug it from the power connection. Also, disconnect it from the circuit breaker.

Step #2: Now unscrew the front cover of the heater to gain access inside. 

Step #3: Locate the high-limit switch from the top of the burner assembly. Locate the resettable red button on the switch and press it firmly.

resettable red button of mr. heater big maxx

Step #4: You will hear an audible “click,” signifying that it has been reset successfully. This allows you to restart the unit.

Step #5: When done, set the cover panel back in and restore the power supply to your heater.

3. Clean The High Limit Switch

In most cases, the malfunctioning high-limit switch is the culprit itself. The best chance is that it is clogged up with soot or dirt buildup. If that is so, the switch may falsely trigger even when it is not supposed to do so.

When the switch triggers, the control board catches it as a fault and throws the error code. A thorough cleaning can help you get rid of this flash code.

Here is how to clean the high-limit sensor of your Mr. Heater Big Maxx garage heater:

Step #1: Start by turning off the power supply of your heater and locating the high-limit button. Follow the above instructions if required.

Step #2: But one thing to note is that, in most models, you may find the switch screwed into the compartment. Simply remove the screws and pull the high-limit sensor straight out, as shown in the image below:

high-limit sensor of mr. heater big maxx

Step #4: Avoid touching the sensor; it’s better to hold it from the base. Now take a fine-grit sandpaper or a scouring pad and gently clean the switch. Avoid using steel wool in this instance, as it can scratch the sensor surface.

Step #5: After cleaning, screw the sensor back into the connection and hope that you will find it working again and that it will eliminate the flashing error codes.

4. Check If The Fan Motor Is Running

A blower motor is an essential component that plays a major role in circulating air throughout the system. It helps to push hot air out of the unit and allows the heating components to be at a stable temperature.

But in the case of Mr. Heater 4 flash codes, the best possibility is that the fan motor is not functioning as it should, leading to an increased temperature in the unit and tripping the high limit sensor.

fan motor of mr. heater big maxx

So as with igniting a flame in the burner, check and inspect if the fan is running. If not, you can be sure the problem lies here.

For instance:

  • First off, check and ensure that the neutral wire of the blower motor is properly connected with the supply voltage neutral.
  • If there are, check for blockages in the fan blades and fan motor. Carefully vacuum the fan blades, housing, and motor using a soft brush attachment and remove any loose dirt or debris.
  • Inspect the fan blades to see if they have become bent or worn unevenly. At times, this may lead to a fan-running issue.
  • In severe cases, you may find the entire blower fan motor fails and needs replacement.

5. Inspect The Control Board

If the blower motor is all good, a malfunctioning control board is another big factor to blame if your garage control board LED flashes 4 times and prevents the unit from functioning.

Bad wiring connections, voltage issues, or worn-out accessories on the control board could be responsible here.

Here is how to inspect the control board:

  • First, examine and make sure all the wiring connections to the control board are well-secured and there are no signs of scorch marks or melted accessories.
  • Now take a voltage meter and measure the voltage between the ACC terminals.
  • It should give a reading of up to 120 volts. If it does not, you can be sure that the board is bad and needs replacement. Get professional help to replace your control board.
mr. heater big maxx control board 

What If My Mr. Heater Big Maxx High-limit Or Flame Roll-Out Switch Keeps Tripping?

Well, after resolving the above factors, it is not uncommon for the high-limit switch in your garage to trip again and throw the error code on the controller.

If your heater’s high-limit sensor keeps tripping, here are some possible factors to check with their recommended solution ideas:

1. Poor Air Flow

Overheating is a common issue in any gas furnace, and it is even more critical for any old HVAC system that is rarely serviced. For instance, the best possible reason is poor airflow or airflow issues in the system.

When the inside combustion gas fails to pass through the unit, it’s obvious the internal temperature exceeds, which leads to the high limit switch tripping so often due to overhearing.

If you are struggling with the constant temperature rise of your HVAC systems, here are two major factors that you must concentrate on now:

i) Clogged Venting

The venting is a passageway that is used to pass the flue gases out of the appliance. After extended use, the vents of the heater may clog up with a large amount of soot or dirt, which blocks the gases from flowing normally.

This builds up heat inside the unit and trips the high limit switch or flame rollout switch to shut down the system.

How To Clean:

Turn off the heater first and allow it to fully cool before servicing the vent. This prevents the risk of burning yourself. Now inspect the vent pipe for any blockages.

  • Use a wire brush to scrub the interior of the vent pipe thoroughly. This will help loosen soot and debris caked on the sides.
  • When done, use a vacuum cleaner to vacuum out any loose debris or soot from the surface. To reach the irregular surfaces, a vacuum cleaner with a brush attachment on the end could work best.
  • When cleaning is done, reassemble the vent piping, making sure the joints are tight and properly connected.

ii) Malfunctioning Blower Motor

A malfunctioning blower motor is another major factor that can be to blame if there is poor airflow in your Mr. Heater Big Maxx system.  Issues like bent fan blades, misaligned motor shafts, or clogged fan assemblies can make the blower motor inactive, making it perform inefficiently.

When this happens, the fan fails to push heated air into the system and degrades its ability to pull fresh air for consumption. This will increase the inside temperature.

In the worst case, you may encounter that the electrical shorts blow the motor circuit fuse or breaker and cut power to the motor entirely.

How To Fix:

In the first troubleshooting phase, we provided the needed instructions to deal with a malfunctioning blower motor. If it is not operating at all, you will need to replace it. Call a professional HVAC technician for further discussion.

2. Dirty Flame Sensor Rod

The flame sensor rod is an essential element of a gas furnace that is designed to confirm there is a flame when the gas valves open. Typically, it is attached to the high-limit switch assembly and regulates the system temperature.

But if the flame sensor is dirty or clogged up, it will fail to detect the heat or temperature from the burner, which will trip the high limit switch. This may lead to 2 flashes on your Mr. Heater Big Maxx as well.

Don’t worry! A thorough cleaning will be enough to save you from this trouble. Here is how you will do so:

How To Clean Flame Sensor Rod:

Before considering anything else, make sure you have turned off the power supply to your heater.

Remove the access panel and locate the flame sensor rod in the high-limit switch assembly. If required, go through your Mr. Heater Big Maxx manual.

Get an abrasive material like steel wool or sandpaper and gently scrub away the soot and other materials clogged on the rod.

Tip: Avoid touching the rod, as it can leave oil and make it fail after reinstalling. Also, it’s best to inspect and clean out the rod at least 1-2 times a year to ensure its functionality is in top condition.

3. Low Manifold Gas Pressure

Low manifold gas pressure is another major factor that causes the high-limit switch to keep tripping. Low manifold pressure means less fuel is getting to the burners. This can lead to incomplete combustion, where not all of the fuel is fully burned.

The unburned particles and excess air from poor combustion mix poorly, resulting in the inside temperature rising and tripping the high limit switch.

How To Fix:

Check and measure the gas flow to your heater system. Make sure it is a minimum of 5.0” w.c. for natural gas. And in the case of LP/propane gas, it should be a minimum of 10.9” w.c. for proper unit operation.

If not, adjust the gas pressure with the help of a professional.

4. Defective High Limit Switch

If you are still struggling with the Mr. Heater high-limit switch failure that keeps tripping again and again, I can bet you are dealing with a bad switch itself. You are not alone here.

Thousands of users find their malfunctioning switch to be the only responsible factor for tripping it prematurely and showing the 4 flashing codes on the control board. For instance;

Phase #1: Test The Switch

You can test the switch to confirm that it is defective. To do so, get a multimeter and set it to the ohms (Ω) setting. Now take out the high-limit switch from the connection and set probes on the switch terminals to check the continuity.

test the switch by multimeter

If it shows a very low resistance, like within 0, 1, or 2Ω, then relax! Your high-limit switch is in good condition.

But a high resistance is the clear signal of the defective switch, which you need to replace as soon as possible.

Phase #2: Replace The Faulty Switch 

When you confirm that you have a defective high-limit switch, you will need to replace it. Though it is technically possible to replace the bad switch on your own, we recommend seeking professional help if you don’t have significant experience in electrical work or heater repair tasks.

How Much Does It Cost To Replace High-Limit Switch In Mr. Heater Big Mxx [DIY VS Professionals]

Well, you can do the high-limit switch replacement job by yourself or with professional assistance. A Havac professional will charge between $150 and $400 to replace the high-limit switch on your heater. The high-limit switch will itself cost between $12 and $50.

But if you already have the replacement high-limit switch and have enough technical knowledge, you can do the job by yourself. This will save you a minimum of $100–$150.

Pro Tips To Prevent 4 Flahses & Other Major Error Codes In Mr. Heater Big Maxx

While operating your Mr. Heater Big Maxx, it is quite common that you encounter the 4 flashes and several other codes in the control board LED. Lack of maintenance and improper operation of the system are normally responsible for such occurrences.

But with some expert tips, you can easily keep your heater limit switch as well as prevent many potential malfunctions in your Mr. Heater Big Maxx.

For instance:

  • Ensure good airflow throughout your heater system, as an airflow issue is the main culprit that may cause your limit switch to break down.
  • Periodically inspect the air passageways of your heater for any blockages and clean them thoroughly.
  • At times, damaged or improperly aligned burners can create hot spots that overheat the limit switch area. So don’t miss inspecting these areas once or twice a year.
  • Ensure to maintain a proper gas flow and combustion process in the unit.
  • As with other steps, special attention is paid to the blow-motor operation. It should turn on promptly when the burners ignite to avoid overheating the cabinet.


Can you bypass your garage furnace high-limit switch?

Yes, you can bypass the high-limit switch of your gas furnace, but only for testing purposes. However, it is not recommended to leave it bypassed for a long time, as it could cause more damage to the unit.

What does 2 flashes mean in Mr Heater Big Maxx heater?

If your Mr. Heater Big Maxx control board LED flashes twice, it is a clear indication of a system lockout failure. The error code signifies that the heater controller is failing to detect or sustain the flame.

Why is my Mr Heater Big Maxx not igniting?

One main reason your Mr. Heater Big Maxx won’t ignite is because the pressure sensors are blocked, which will prevent the burner from igniting. Other major reasons include faulty flame sensors, blown fuses, or malfunctioning inducer motors.

In Closing

A blinking pattern of 4 flashes on the status light of a Mr. Heater Big Maxx furnace indicates a problem with the unit shutting down due to high temperatures. This is typically triggered by the high-limit switch, which trips to protect the heater from overheating dangers and ensure your safety.

The troubleshooting steps you need to take are: inspecting the vents for blockages; cleaning the blower motor; and ensuring proper gas flow to the unit as recommended.

Throughout this discussion, we have gone over all of the above procedures in depth. Even so, feel free to leave a comment if you have any questions regarding this matter. Our HVAC specialists are here to help you at any time.

About David

David is a man who loves doing research and finding out the best solution to any type of heating appliance issues like heaters and fireplaces. Whenever he finds the perfect solutions to any issues of heating appliances after doing in-depth research, he loves to share them with his readers. In fact, his aim is to help his readers to fix the issues with their heating appliances easily.More about us .

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