Why Does My Flame Rollout Switch Keep Tripping?

Resetting the furnace rollout switch can fill your mind with worries, and for a good reason – it’s usually a sign of a significant underlying problem. Moreover, resetting the switch often feels like you’ve just escaped a major disaster. 

It would be best to try to prevent issues that may cause the rollout switch to trip for the above reasons. And if it trips at some point, the most important thing is not to switch it back ON but to fix the underlying issue. 

Below, we discuss the most common reasons the flame rollout switch may trip, symptoms of a tripped rollout switch, and what you can do it. Let’s begin with a brief overview of flame rollouts and how flame rollout switches work. 

What Causes Flame Rollout?

A flame rollout is when flames roll out of the combustion chamber of your gas furnace. The rollout is typically caused by the interaction between flames and combustion gases in the gas chamber. 

When the furnace is up and running, it sustains a flame that’s meant to provide heating for our home. However, under normal circumstances, the flames are meant to remain within the walls of the combustion chamber. 

Unfortunately, sometimes inflammable gases can build inside the gas chamber, preventing oxygen from getting to the flames below. The buildup of gases is caused mainly by soot buildup. Excessive soot can prevent gaseous byproducts from leaving the combustion chamber. 

As these inflammable gases build up, they cut the oxygen supply to the flame below – which critically needs oxygen to keep burning. 

So, what follows? The flame has to try every means to find the oxygen it needs. Thus, the flame may sometimes roll out of the combustion chamber to reach the oxygen just above the layer of soot outside the combustion chamber. 

Another common cause of flame rollout is a blocked flue pipe. The flue pipe is a small vent that releases combustion gases outside the combustion chamber. When the vent is blocked, combustion gases cannot escape outside the furnace. This often leads to the buildup of incombustible gases within the furnace, eventually leading to flame rollout.  

Flame Rollout Risks

Flames rolling out of the furnace gas chamber is extremely dangerous. For one, it puts your life and the lives of your loved ones at risk. What if the “floating flame” reaches a flammable item and catches fire? It creates massive danger and could potentially burn down the house. 

Moreover, even if the flying flames don’t burn the house, they may reach parts of the furnace not designed to handle the high levels of heat or open flames. This can result in accelerated furnace degradation, leading to expensive repairs or replacements. 

Finally, flame rollouts can also point to serious underlying issues that may put you and your family at risk. For instance, sometimes rollouts happen because of a cracked exchanger. A cracked heat exchanger creates a significant risk for carbon monoxide leaks – a poisonous gas that can cause asphyxiation and even death. 

What’s a Flame Rollout Switch?

The flame rollout switch is a safety mechanism built into furnaces to protect you and the furnace in case of a flame rollout. It shuts down the furnace immediately it detects a flame rollout to prevent potential fires. 

How it works is pretty straightforward. The rollout switch is wired to the circuit of your furnace’s internal power source. Thus, it cuts off power to the furnace when it trips, causing the furnace to shut down. 

The switch is located near your furnace’s burner box. It’s a rounded device with a switch sticking out of the top. You’ll be able to identify it thanks to the two metal strips, about an inch each, attached to each side of the switch. The strips have holes at the tips furthest from the switch. 

Fortunately, you can reset the switch yourself when it goes off. You need to press the center button. However, it’s usually advisable to fix the underlying issue first. 

What Causes Flame Rollout Switch to Trip?

Although it primarily monitors flame rollout and will instantly go off when a rollout is detected, the flame rollout switch can also be tripped for a few more reasons. Here’s what you need to know;

1. The flame has rolled out

This is the primary reason the rollout switch will trip. If it detects flames outside the pre-defined regions of the furnace, it will go off right away to prevent a potential fire. 

As we’ve seen, a flame rollout can happen for many reasons. Perhaps you have a blocked flue that keeps combustion gases within the gas chamber. Or maybe it’s a cracked heat exchanger. Whichever the case, if there’s a flame rollout, the switch will trip. 

2. Overheating 

Sometimes the rollout switch may also trip if overheating is detected in certain parts of the furnace, even if there’s no flame rollout. For instance, if areas beyond the heat exchanger become extremely hot, they may catch fire. The rollout sensors will treat it as a rollout event and trigger the rollout switch. 

Overheating can result from many events. For instance, it may be the result of an undetected flame rollout. Also, it could be a sign of a bad heat exchanger. The heat exchanger’s primary function is to contain the heat within the furnace. Therefore, a bad exchanger may allow excessive heat to reach other parts of the furnace. 

3. You have Low Gas Pressure 

You’re probably wondering how low gas pressure can cause the rollout switch to trip. It’s easy. If you have low gas pressure, the flame retreats from the burner port back into the burner body. Sometimes it may retreat to the burner orifice. 

This is extremely dangerous as overheating the orifice can cause the internal components of the gas to fail. It’s also a lot more challenging to control a flame burning deep inside the orifice.

Above all, it constitutes a flame rollout because the flame would be burning outside the designated zone. Thus, it’s enough reason to trigger the rollout switch. 

Symptoms of a Tripped Rollout Switch

Knowing when the flame rollout switch is tripped isn’t as straightforward as you’d wish. You’ll need to be highly observant. Check out for the following;

  • The burner goes off

This is obvious. As we’ve seen, the rollout switch is wired to the furnace circuit board and works by disconnecting power to the board to shut off the furnace. Therefore, the first thing that will happen when the rollout switch is tripped is that the burner will go off. 

  • The blower fan keeps running

In addition to the burner going off suddenly, you want to listen out for a humming blower fan. Gas furnaces are programmed such that if overheating or a flame rollout is detected, the blower fan remains ON for a while longer to cool the unit down. Unless you shut off the furnace, the blower fan will keep running until the furnace reaches a pre-determined temperature. 

  • The button on the switch is popped

Most rollout switches are “one-time” switches. Once the switch trips, you have to replace them. However, others have a button in the middle that pops up when the switch is tripped. You can pop the button back into position to reengage the switch and reset the furnace for the latter. Just be warned that doing so without addressing the underlying issue can cause even more problems down the line. 

  • Control board blinking error code 

This also doesn’t apply to all furnaces. However, some are designed to blink pre-determinedly to alert you that the rollout switch has tripped. The light will blink a specified number of times, depending on the manufacturer. Cross-check with the user manual to verify the issue. 

  • The burner won’t stay lit 

It’s natural to try to relight the furnace when it goes out. It will not stay lit if the rollout switch is tripped. Why? Because, as we’ve seen, a tripped rollout switch cuts supply to the board. Thus, you can only resume heating after switching the rollout back ON. This means that the burner will go off within seconds of relighting it until you switch back the rollout switch.

How to Test a Rollout Switch

You can easily test whether your rollout switch is working using a multimeter. Multimeters cost about $30 at the store. 

How to Fix Furnace Flame Rollout Switch

Fixing a flame rollout switch isn’t difficult. However, the exact fix will depend on the type of switch and type of damage. 

If dealing with “pop-up” switches that pop out of the socket when the switch is tripped, you need to pop the top part back to reset the heater. However, if it’s a one-time switch, you need to replace it because it won’t work after tripping. It’s best to find an HVAC pro for the installation. 

Flame rollouts are extremely dangerous. You must never take them for granted. You should take every precaution to prevent gas furnace flame rollouts. However, if it happens, the rollout switch will help keep you and your loved ones safe. 

Leave a Comment