Mr Heater Big Maxx System Lockout [5 Easy Solutions]

Commonly, when Mr. Heater Big Maxx system lockout occurs, the heater’s LED light keeps flashing twice. This is an error message that indicates a failure of flame detection or a weak flame that won’t stay lit. 

mr heater big maxx system lockout

To get your system out of lockout mode, you need to get rid of this error code and reset your heater.

The common issues causing system lockout are dirty or malfunctioning pilot assembly, clogged or broken flame sensor, faulty thermocouple, an air leak in the gas line, and insufficient gas supply.

We’ll help you with simple solutions to each of these problems. Just keep on scrolling!

Mr Heater Big Maxx System Lockout [5 Easy Solutions]

In this section, we’ll explore why your Mr. Heater Big Maxx is having a system lockout and how you can fix this Mr. Heater Big Maxx issue simply.

1. Dirty or Malfunctioning Pilot Assembly

A pilot flame that isn’t strong or won’t remain lit indicates a dirty or malfunctioning pilot assembly. In that case, your heater will diagnose this issue and enter the system lockout.


The first thing you should try is to clean your pilot assembly. Here’s how to do it:

Step 1: Close the main gas valve and turn off the fireplace. Allow it to cool before touching it. Examine the tube where the pilot flame emerges with a flashlight. 

You’ll notice a little tube snuggled inside the larger one with a tiny hole. If you can’t see the tiny opening at all, or if you can see it but it’s clogged with debris or dust, it’s possible that you just need to clean it.

Step 2: Blow the dust and grime off the end of the innermost tube with compressed air from a can. With the flashlight, check to see if all of the dust has been removed.

Step 3: Reopen the gas valve and try to relight the pilot. In case, the pilot is still not working, turn off the main gas valve. Unscrew the nut at the base of the pilot assembly using a tiny adjustable wrench to remove the complete pilot assembly.

Step 4: Blow compressed air into the back of the pilot assembly, directing the flow toward the pilot flame tube aperture. Using the adjustable wrench, reinstall the pilot assembly. Make sure the nut is securely fastened.

Step 5: Restart the gas valve and try to relight the pilot light. Contact a gas fireplace service technician to clean or, if necessary, replace the pilot component if it still won’t light properly or at all.

2. Clogged Or Broken Flame Sensor

For the gas valves to open in order to ignite the main burners, the flame sensor has to detect the pilot flame. It’s a safety feature that ensures no gas has spilled. You need to inspect the pilot light to make sure that this is what’s causing the error.

You most certainly have a problem with the flame sensor if the pilot flame is lighted and you’re still getting the error message that is locking out your EcoSmart water heater. 


Remove the flame sensor and examine it. If it’s unclean, clean it well. A flame sensor that has been fractured or cracked must be replaced the flame sensor. Make no attempt to bypass the flame sensor.

Doing so can be quite hazardous. You don’t want to lose your home over saving a few dollars.

3. Faulty Thermocouple

A faulty thermocouple is a typical problem that causes the pilot light to flicker or go out completely. This could be why your heater is in lockout mode. 

You can use a multimeter to confirm that the thermocouple is the problem. If the reading on the meter does not display 12mV or more, your thermocouple is broken.


A broken thermocouple can only be fixed by having replaced the thermocouple. It’s possible that you’ll need to hire an expert. However, if you have some technical expertise, you can fix your heater by watching the video below.

4. Air In Gas Line

If there is air in the gas line, the pilot will not light properly. This will result in a system lockout.


To get your heater up and running again, you’ll need to bleed the air out of your gas line.

5. Inadequate Gas Supply

Your heater is powered by gas. As a result, if you have enough fuel, your pilot won’t stay lit. If this happens, your heater will go into lockout mode. Your gas supply could be affected by a lack of gas, poor gas pressure, or dirt in the gas line.


It’s a good idea to make a quick inquiry at your gas utility company and have them look at your problem. They’ll be able to assist you.

How To Reset Mr. Big Maxx Heater?

It’s very simple and easy to reset your Mr. Heater. You can do it on your own. After you’ve solved the issue that is behind the error message, perform the following procedure.

To break the lockout, all you need is to move the thermostat from “HEAT” to “OFF”. After that, you’ll again need to turn the dial to “HEAT”. Your heater will reset and should no longer be in lockout mode.


Can you use a Mr heater in a closed garage?

A propane heater should not be used in a closed garage for safety concerns. In the event of an emergency, ventilation is required. If you have to use it in a confined space, never leave it unattended.

How many BTU do I need for a 2-car garage?

In the case of forced-air heaters,  a two- to a two-and-a-half-car garage, a 45,000 BTU garage heater is recommended. While, according to the manufacturers of low-intensity infrared tube heaters, 30,000 Btu can heat a garage of the same capacity. 

Which buddy heater is the best?

Our favorite is the Mr. Heater Portable Buddy. It’s their mid-sized heater, and it’s ideal for heating a tent or room of any size. It’s lightweight, comes with two heat settings, and has a foldable handle.

Can you use a propane heater without a regulator?

No. Too much propane can flow into the heater without a regulator, resulting in an explosion. A pressure regulator is required for a propane heater in order to regulate the amount of propane flowing into the heater.

How long will a 20 lb propane tank last at 50000 BTU?

In general, a 20-pound propane tank with a 50,000 BTU rating will last between 6.31 and 8.41 hours (see full calculations and details below). On a 20-pound propane tank, the most efficient propane patio heaters can run for roughly 8 hours.


Hopefully, with our guide, you can now fix your heater and get it out of lockout mode. In case you have questions, leave us a comment below. We’d love to help you. 

About William

William is the founder of He has real life practical skills in fixing smoker & heating appliance issues. He loves to share his knowledge & helps others in fixing their appliances & saving their money. William firmly believes that anyone can repair his or her unit with the correct guidance & knowledge. See more at about us.

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