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Why is My Direct Fired Heater Not Working? Troubleshooting Guide for Your Direct Fired Heater

If you rent heaters for your construction site you know that the equipment might need quick maintenance throughout the winter.

When it comes to direct fired heaters, you may want to try to fix the issue yourself. This could prevent having to pay a service fee from your rental company. Let’s say you show up one morning and you’re wondering why your direct fired heater isn’t working. The following blog will walk you through some quick troubleshooting tips for your direct fired construction heater.

If you’re wondering, a direct fired heater is an open flame heater that is generally used on the construction site. These heaters can also use both liquid propane and natural gas as a fuel source. Direct fired heaters aren’t prone to many issues, so troubleshooting for direct fired heaters is usually pretty simple. These tips will show you some easy things to check before calling in a technician to inspect the issue further.

Diagnosing the Problem

Since direct fired heaters are pretty simple construction heaters, there are a few common issues that could be causing your heater’s problems. These issues can sometimes be easily fixed on your own. You may be able to determine what is wrong with your heater by observing a few things that happen when you’re attempting to start your heater. These symptoms include:

  • The heater won’t turn on at all
  • The direct fired heater won’t light even though the spark plug is creating a spark
  • The direct fired heater won’t light, and the spark plug isn’t creating a spark
  • The heater is lighting and then quickly burning out

The Direct Fired Heater Won’t Turn On at All

Let’s say you turn on your heater and nothing happens. The fan doesn’t run, the spark plug doesn’t spark, and the flame doesn’t ignite.

  1. The first thing you are going to want to check is whether or not your heater is plugged in.
  2. If the heater is unplugged, plug it back in and re-fire the heater.

This might sound stupid, but it happens more than you might think. Heaters can get unplugged from people tripping on the cord, unplugging the cord to plug something else in, or for a range of other reasons. So if you’re heater isn’t powering on, check the power source first.

The Heater Won’t Light, and the Spark Plug is Creating a Spark

So in this instance, you turn on your direct fired heater, the fan starts and the spark plug is sparking, but you’re not getting any flames. At this point you may be dealing with either a bad fuel connection or low fuel levels.



  1. First, turn off your heater.
  2. To diagnose this problem you’ll want to inspect your gas valve on the regulator to make sure it’s on. Walk over to your propane tank and check the valve and confirm that it’s in the on position. If the valve is off, turn it back to the on position and listen for the gas going through the line.
  3. Next check the gas valve on top of the fuel tank to make sure that it is also in the on position.
  4. Lastly, make sure that your fuel tank isn’t empty. Check the frost line on your fuel tank to see how much fuel you have left. If the frost line is near the bottom, you could need a tank re-fill to get your heater firing again. You can also pick up your fuel tank to see how much fuel is left if you can’t see a frost line.
  5. If all of your valves are turned on and you still have fuel, the last thing you’ll want to check out is your fuel hose. If your hose is kinked anywhere it could be stopping the flow of fuel to your heater.
  6. After checking your valves, fuel source and hose, start your heater back up again. If the fan is running, the spark plug is sparking and you still don’t get a flame, call your rental company to have a service technician further diagnose the problem.

The Direct Fired Heater Won’t Light and the Spark Plug Isn’t Creating a Spark

For this issue, you’ll start up your direct fired heater and the fan will turn on, you’ll smell gas but you won’t be getting any flame and your spark plug isn’t sparking. This is probably because you have a dirty spark plug. A dirty spark plug can happen over time when buildup forms on your spark plug so it can’t ignite the gas. You’ll probably see residue on the spark plug that you’ll want to clean off. Follow the steps below to attempt to fix the problem. You’ll need a wire brush to complete these procedures.



  1. First, turn off your heater and unplug it from your power source.
  2. Tip the heater so the barrel faces upward.
  3. Take your wire brush and clean the black residue off of the spark plug.
  4. Once the residue is cleaned off, tip your heater back down and plug it into your power source.
  5. Turn your heater back on and the heater should fire. If your heater still won’t fire, call your rental company to have a service technician further diagnose the problem.

The Direct Fired Heater is Lighting and then Quickly Burning Out

If your heater is turning on and then quickly extinguishing, you might have a dirty flame sensor rod. The flame sensor rod is a simple tool that confirms to the heater that the flame is present when the gas valve is open. It’s a thin metal rod that is located in front of the flame stream. Follow the steps below to diagnose and possibly fix the problem. You’ll need some emery cloth or sand paper to follow these procedures.



  1. Try turning the heater on again. If you turn it on and it lights and then quickly extinguishes again you probably have a dirty flame sensor rod.
  2. Unplug the heater and let it cool down first. Even though your heater may only have been lit for a short time, it’s still going to be hot if you try to touch the interior.
  3. Once your heater is cooled, flip it up so the barrel is facing upwards.
  4. After tipping your heater up, you’ll see the flame sensor rod at the top of the direct fired heater. It will probably be corroded and dirty, which is the reason the heater won’t stay lit.
  5. Take your sand paper or emery cloth and clean off the rod of all dirt and corrosion.
  6. Once your flame sensor rod is cleaned, set it back down, turn it on and fire it back up. At this point the heater should fire. If it still doesn’t call your rental company to have a service technician further diagnose the problem.

If you’re renting a direct fired heater that isn’t working, and want to save yourself a trip from a service technician, there are a few things you can check first. The most common problems that can be easily solved are, no electrical source, no fuel source, dirty spark plug, and dirty flame sensor rod. These issues are really easy to diagnose and fix on site, so there is no need to bring anyone out and possibly incur a charge. If these simple solutions don’t fix your problem, please contact a trained service technician before taking any more action. Remember, these heaters can be dangerous to tinker with if you don’t know what you’re doing.

On Site Companies is a construction equipment rental company out of St. Paul, Rochester, Mankato, Cromwell MN, and St. Louis MO. For more questions about direct fired heaters or renting heaters for your construction site, call us at (651) 429-3781 or email us at [email protected].

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