Tip & How-To about Heating & Cooling

Basic Furnace or Heating System Troubleshooting

If you are not getting any response from your furnace and your furnace is not working, then the first thing you want to check is that there is power coming in.

If you have 120VAC coming in, then check to see if you have 24VAC coming from the transformer. If you do not have the 24VAC from the low voltage transformer then the transformer has burnt out. Power surges and especially brown outs (low voltage) can cause the transformer to burn out.

If there is 24VAC coming from the transformer secondary then check to see if there is a fuse in the low voltage circuit. Sometimes the fuse on the circuit board and often are an automotive type fuse that plugs into the circuit board. Sometimes the fuse will be an inline fuse that will be in a black round tube type holder. If the fuse is blown do not replace with a higher amperage fuse, you will cause more damage, or blow the transformer.

If the fuse is blown then unhook the t-stat wires and check again. This will tell you if the short that blows the fuse is external to the furnace or internal.

Now if all of that checks out then the next thing would be to check the low voltage safety circuit. Things such as door switches and high limit switches are all possibly included in this circuit, if any of them are open the heating system will not work.

As a last resort, the problem could be in the circuit board. They do go bad and can shut everything down also. Most circuit boards will also flash a LED light to give you a code for what is wrong and why the furnace is not working.
Count the number of flashes and then check the inside of the front cover to see what the code represents.

This will give you a basic progression of things that you can check through. Using an electrical meter is essential to being able to diagnose and troubleshoot the heating system. If you do not have one and/or do not know how to use an electric meter proficiently, then find someone to help you that does know how to use one well to help you.

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1 Answer

A carrier furnace model 58dla110---10122 won't start


Make sure the kill switch on the blower door is closed, or furnace won't do anything. Then remove power from furnace for a few seconds, then try again. Still no go? Take a jumper wire and jump the "r" terminal to the "w" terminal on the furnace's board. This bypasses the thermostat. This is only for testing. If it still wont run, call service guy. Gas furnaces are not good things to tinker with.

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my trane xr12 wont run. i checked the capacitor and its good but still nothing is working.


Hello my name is Heath it will be my pleasure to assist you. First thing to do is go to the furnace take off the lower blower door and locate the circuit board turn the power off to the furnace. In the circuit board there should ba a small car like fuse usually 3 or 5 amps check the fuse it is probably blown replace the fuse with the same amperage fuse and then turn the power back on on the furnace and check the operation of the furnace.

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Hello my name is Heath it will be my pleasure to assist you. First thing to do is go to the furnace take off the lower blower door and locate the circuit board turn the power off to the furnace. In the circuit board there should ba a small car like fuse usually 3 or 5 amps check the fuse it is probably blown replace the fuse with the same amperage fuse and then turn the power back on on the furnace and check the operation of the furnace.

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1 Answer

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your thermostat only requires 24 volts. If you are not getting 24 volts, you will have to go to the control panel of your furnace. On newer models, there is a small fuse on the circuit board of the furnace . It will be 3 or 5 amp. Check it first. Make sure you have power to the furnace also. If the blower access door is loose you will lose power to the furnace. These are the first things to check. Good luck.

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