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BillyHvac, Journeyman HVAC Tech
Category: HVAC
Satisfied Customers: 22542
Experience:  Endorsed for unlimited heating, cooling, oil burners, boilers, refrigeration, hydronics
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I have a trane xb furnace 2006. It wont fire the heat just

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I have a trane xb furnace 2006. It won't fire the heat just runs the fan. Red lighting blinks 4 times

Can you tell me if the filter was plugged when this ocurred?


Customer: replied 3 years ago.

No filters should have been ok. Only in for a week or two before trying to flip on heat. Is there a reset just in case

There is not a "reset" for the high limit. It either closes back on its own or not.

The switch is normally closed but opens during high heat situation. Once cooled it is supposed to close by itself but can be stuck.

On the front wall of the furnace is flat plate with just 2 wires attached. Do you see this plate?

Customer: replied 3 years ago.

Think so it has two yellow wires on it. Brown backing with two little nuts


First turn off power.
Tap that switch briskly 3-4 times.
Turn power back on and tell me code


Customer: replied 3 years ago.

Still flashing 4 times

thank you

now turn power off
remove the 2 wires from plate
use a short wire or paperclip and stick into the end of each wire thus joining them.

hold any exposed metal away from furnace cabinet and turn power on.

Tell me if 4 code remains. Then we move to next step.

Customer: replied 3 years ago.

I think I made good contact. Still flashing four

Thank you.

What is the actual model number of the unit and I will pull wiring to see if there is a secondary limit

Customer: replied 3 years ago.



This unit has a few in series.

They leave the circuit board on terminal HLO (high limit out)....follow thee wire through all the limits in series. If there is a push button in center press the small button firmly. Follow this wiring and switches until it returns to HLI (high limit in).

Something between HLO and HLI is reading open.


Customer: replied 3 years ago.

Well no resets only the switch we started with and two little button looking switches one on top and one on bottom of where the fire should be. Can I remove the first switch that I beat on and replace it?

The 2 little button switches willhave a small reset center switch.

The objective here is to see if a limit is open....or if the limits are all closed but the board is bad.

Do you have a voltmeter?

Customer: replied 3 years ago.

I do not. So that tiny peg on the middlebis a reset swithch? Should I push it with a paperclip


Press the center tab firmly and tell me if there is a click

Customer: replied 3 years ago.

May have gotten a small click from the bottom one. Hard to tell. At this point I am about ready to give up.

Customer: replied 3 years ago.

May have gotten a small click from the bottom one. Hard to tell. At this point I am about ready to give up. Open lint device is the code

Turn unit back on and tell me code.

We can try one more thing and then we will call it a day.
Customer: replied 3 years ago.

Ok what's ya got

Take the wire that leaves hlo....take it off the first switch it goes to. Then take the wire from hli from the switch it goes to....

Then put the hli and the hlo wire direct together.

This (for testing) bypasses the limit circuit.

Customer: replied 3 years ago.

Jumped both and still get my 4 lights

Thank you.

Then it makes sense if this happened when filter was is a circuit board issue.

The power leaves hlo and gets back to hli but the board does not recognize it.

The only fix is to replace the circuit board.

I thank you for your patience!


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