Otis Singleton
A faulty thermostat can be the reason why your furnace is not turning on, even when your house is cold. You can temporarily bypass the thermostat to get your furnace working again. However, it is important to note that this will cause your furnace to run continuously, wasting energy and potentially causing your system to overheat and fail. To bypass the thermostat, you will need to turn off the breaker to the furnace and locate the red and white wires attached to two screws on the thermostat. Loosen the screws and disconnect the wires. You can then bypass the thermostat by touching the wires to the red wire, which supplies power. If you have a two- or three-wire thermostat, use the white wire. It is important to never touch the red wire to the blue or black common wire, as this could blow a fuse.
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What You'll Learn
Turn off the breaker to the furnace
Turning off the breaker to the furnace is a crucial step when attempting to bypass a thermostat on an electric furnace. This step ensures that the power supply to the furnace is interrupted, allowing for safe adjustments to the system. Here are some detailed instructions and considerations to keep in mind when turning off the breaker:
First and foremost, locate the breaker box or circuit breaker panel that houses the furnace's circuit breaker. This is typically located near the furnace or in a utility area of the building. Before proceeding, ensure that you have shut off the correct breaker by identifying the one labelled specifically for the furnace. This is important because shutting off the wrong breaker can lead to issues such as a blown fuse.
Once you have identified the correct breaker, proceed to turn it off. This is usually done by flipping a switch or moving a lever to the "off" position. In some cases, you may need to apply light pressure to move the breaker to the off position. Be cautious, as attempting to force it with excessive force could indicate an underlying issue.
If you are dealing with a gas furnace, special considerations must be made regarding the pilot light. In some older installations, turning off the breaker can cause the gas valve to close and the pilot light to go out. However, in newer furnaces or those with a thermocouple or thermopile setup, the pilot light may remain lit even when the breaker is off. Be prepared to relight the pilot light if necessary, and consult the furnace's manual or a licensed HVAC professional if you are unsure about the specific setup of your furnace.
After turning off the breaker, it is essential to allow the furnace time to cool down. Even with the power interrupted, the furnace may still retain residual heat. Wait for a few minutes before proceeding with any further adjustments or maintenance to ensure your safety and avoid the risk of burns or damage to internal components.
Turning off the breaker to the furnace is a fundamental step when bypassing a thermostat. However, it is important to exercise caution and follow proper procedures to avoid damage to the furnace or safety hazards. Always consult a professional if you are unsure about any aspect of the process.
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Locate and disconnect wires
Before attempting to locate and disconnect wires, it is important to turn off the breaker to the furnace. This is done by locating the breaker and flipping it to the "Off" position. Once the power is off, you can proceed to remove the thermostat cover. On some models, this may involve popping off a plastic cover, while others may require unscrewing a couple of screws. With the cover removed, you will be able to access the wires attached to the thermostat.
The next step is to locate the specific wires that need to be disconnected. In most cases, you will be looking for the red and white wires attached to two screws on the thermostat. Using a screwdriver, loosen the screws and unwrap the wires. It is important to be cautious and careful during this process to avoid any potential risks or accidents.
In some cases, you may encounter different wire colors, such as black and yellow wires. It is crucial to properly identify the wires before proceeding. Incorrectly disconnecting wires can lead to short circuits or blown fuses. Always verify that you are working with the correct wires for your specific furnace and thermostat setup.
Once the correct wires are located, you can proceed to disconnect them. This typically involves unscrewing or unfastening the wires from the thermostat. Ensure that you have a safe and proper place to set aside the disconnected wires, keeping them away from any conductive materials or sources of heat.
After successfully disconnecting the wires, it is important to understand the implications. By disconnecting the wires and bypassing the thermostat, the furnace will run continuously. It will only shut off if you manually disconnect the power source or intervene with the wiring. This can lead to energy wastage and potentially cause your system to overheat, so it is important to be mindful of these consequences.
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Use red wire to supply power
If you want to bypass a thermostat to test it, you can use the red wire to supply power directly to one of the other wires (except the common wire). The red wire is the standard colour of the wire that supplies power to the thermostat. It is marked with an 'R' on the furnace board. The R wire usually connects to the red wire from the furnace, which is the 24-volt power wire from the furnace transformer.
If you have a two- or three-wire thermostat, use the white wire. In a two-wire system, you have no choice, and if there are three wires, the system is usually designed for the blower to come on automatically when the thermostat calls for heat. Twist the R wire together with the wire you chose and then turn the breaker back on.
If you chose the green wire, you should hear the blower in the air handler come on as soon as you flip the breaker. If you chose the white wire, you'll hear the furnace and blower start simultaneously.
If your thermostat is dedicated to air conditioning only, it will have a red Rc wire. For heating and cooling systems, it will have a red Rc and a red Rh wire. Though both wires are red, they are not interchangeable. For the thermostat to work properly, the red wires must be connected to the correct corresponding terminal.
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Adjust low pressure
If your unit is a pump-down unit, you can use low pressure as your thermostat. Adjust the low pressure to the corresponding temperatures. As this is a cooler, adjust the cut-out to 35 degrees converted from pressure and the cut-in to 40-42 degrees. You will need to know how to use a PT chart.
For example, if your unit is R404a, you can have a cut-out of 85 psig with a differential of 25-35. Or, if the low-pressure control allows, a cut-out of 85 psig and a cut-in of 55-65 psig. This won't be perfect, but it will work temporarily.
You can also adjust the LPCO to ensure the compressor doesn't pump into a vacuum after bypassing the thermostat. This can be done by using the black and yellow wires with a wire nut, leaving enough slack to re-splice the wires when needed.
Remember, these are temporary solutions, and you will need to replace the part and change the low-pressure settings back afterward.
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Reset when new controller arrives
Resetting the thermostat when your new controller arrives involves reversing the bypass procedure and reconnecting the wires to their original configuration. Here's a step-by-step guide to help you reset your thermostat safely:
Locate the 240-volt double-gang breaker in the main electrical panel. This breaker typically controls most HVAC systems, including the furnace, regardless of their specific components. Turn off this breaker to cut power to the thermostat.
Using a flathead screwdriver, carefully remove the thermostat's cover plate. This will expose the wires and connections behind it. It's important to be gentle during this step to avoid causing any damage to the wires or the wall.
Identify the wires that you previously used to bypass the thermostat. For example, in a previous bypass procedure, you may have used the yellow and black wires, or the red and green wires, depending on the specific bypass method chosen.
Untwist the wires that were previously twisted together as part of the bypass. Ensure that you separate them carefully and that none of the wires remain connected.
Now, you'll need to reattach the wires to their original terminals. Refer to the schematic or diagram of your thermostat wiring to ensure that each wire is connected to the correct terminal. This step is crucial for restoring the proper functioning of your thermostat.
Once all the wires are securely connected to their respective terminals, carefully replace the thermostat's cover plate using your screwdriver. Ensure that it is securely attached.
Finally, turn the breaker back on to restore power to the thermostat. At this point, your thermostat should be functioning normally, and the bypass procedure should be reversed.
It is important to note that bypassing a thermostat is generally a temporary solution and not a long-term fix. Always consult a professional HVAC technician if you are unsure about any part of the process or if you encounter any issues during the reset.
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Frequently asked questions
Turn off the breaker to the furnace and locate the red and white wires attached to two screws on the thermostat. Disconnect these wires and your furnace will be temporarily bypassed.
If you have a two-wire thermostat, use the white wire. If there are three wires, the system is usually designed for the blower to come on automatically when the thermostat calls for heat.
Do not touch the red wire to the blue or black common wire as this is likely to blow one of the fuses in the control board.
