Can I bypass the flame rollout switch on my furnace?
Yes, you can.
But it is a bad idea – even for a “little while” until you can get a new one installed.
The flame rollout switch is a safety device that can prevent a furnace with a defect from overheating and damaging expensive control components or the heat exchanger. Wreck the heat exchanger, and you’re looking at $1,000+ repair or the need for furnace replacement.
That’s putting the furnace in harm’s way. You’ll put yourself there too, since an overheated furnace can catch fire and/or release poisonous carbon monoxide gases into your home.
Long story short, to do anything to bypass this safety feature is to incur serious risk to your furnace, your family and your home.
Explaining Flame Rollout on a Gas Furnace
What is flame rollout?
When a gas furnace is operating properly, the flames from the burners are drawn into the heat exchanger by the draft caused by the draft inducer fan – the fan that pulls in fresh combustion air and pushes exhaust gases out the vent.
These flames burn at almost 2,000° F, and they begin heating the heat exchanger very rapidly before passing on to the flue and out of the building. There are several conditions - including a partially clogged flue or a cracked heat exchanger – that can result in these very hot flames being pushed backward out of the furnace’s combustion box instead of into the furnace. This is called flame rollout because the flames have “rolled out” of where they were supposed to go. They are going the wrong way.
When flame rollout occurs, much of the heat from the flames immediately begins to threaten the wiring, control board and other sensitive components that are not able to withstand a lot of heat. If not stopped, this heat can cause severe damage within minutes.
The Purpose of the Flame Rollout Switch
The flame rollout switch (your furnace may have more than one) is located in the area near the sensitive components. It is designed to detect heat in excess of about 350° F, i.e., it detects flame rollout.
When this occurs, the switch will trip and shut off the gas valve, which will cause the flames from the burners to go out. No fuel, no fire.
Once the rollout switch has been tripped, the furnace will not respond to a signal from the thermostat calling for heat. An error code that indicates a flame rollout problem will be blinking on the control panel in the furnace. Normally, when the occupants realize that their furnace is not coming on, they will call a local HVAC technician who will be able to diagnose and fix the problem.
But some of us – and many of our knowledgeable Pick HVAC readers, prefer DIY when possible.
Resetting the Flame Rollout Switch
Most flame rollout switches have a reset button. When tripped, the button pops up. It can be reset by pushing it back down until you hear a click. This might take a bit of effort. If the switch doesn’t click, then it hasn’t been tripped – and your issue is something else.
There can be an occasion where the switch tripped for some unexplainable reason that was not caused by an actual rollout or was caused by temporary flame rollout. For example, if snow on the roof is covering the vent, this could cause flame rollout and a tripping of the switch. That’s an easy fix. In fact, hot flue gases normally melt the snow in minutes, solving the issue.
This might be an unusual situation, but not impossible.
Reset or call for help? Some HVAC experts recommend that if your flame rollout switch has tripped, you should immediately call a knowledgeable technician to diagnose the problem. There’s nothing wrong with that approach.
Others say you can reset it up to three times before calling for help. We would recommend that you reset it no more than once. And if there is a possibility of a temporary blockage of the vent, and you’re comfortable exploring that potential in a safe manner, consider doing that if you’re committed to checking for solutions before calling a furnace technician.
OK – But Should I Bypass the Flame Rollout Switch?
We can’t recommend that approach to furnace troubleshooting. The switch is like brakes on a vehicle. You need brakes the most when there is a reason to stop the vehicle. It’s the same with the flame rollout switch.
The many HVAC experts we know agree that the flame rollout switch should never be bypassed by a homeowner or renter. On occasion, for testing purposes only, a trained HVAC technician may bypass a rollout switch temporarily, but that procedure is something that only a pro should do.
The reason should be obvious, but here it is anyway: to bypass a flame rollout switch is to invite the very real danger of burning up your furnace or even burning down your home. It would be like putting a piece of black tape over the “Engine Overheat” light on your vehicle’s dashboard because you didn’t like the red light shining in your eyes. Once again – don’t bypass a flame rollout switch.
Can I DIY Flame Rollout Switch Replacement?
Sure. If you watch the burners in action, and the flame is being drawn into the furnace interior, yet the rollout switch keeps tripping, maybe that’s the issue. Flame rollout switches cost less than $10 to about $40, and they are easy to replace. Keep in mind that you can return electronic parts that have been installed – so be prepared to lose the money you’ve invested in the part. If you have a multimeter, test the old part for continuity. If the switch is good, the meter will read 0 ohms. You can re-install the switch and return the other.
If the switch is bad – stuck open – the multimeter will read infinite resistance. This short video shows how to find, remove and replace a flame rollout switch.