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M Oglesby
M Oglesby, HVAC Technician
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Experience:  Universally Certified HVACR Technician
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My furnace light is blinking 4 times and the panel says its

Customer Question

My furnace light is blinking 4 times and the panel says its open high limit device what does that mean?
Submitted: 3 years ago.
Category: HVAC
Expert:  M Oglesby replied 3 years ago.

M Oglesby :

This is saying that either your Main Limit or Manual reset rollout limit switch is open.

M Oglesby :

These switches monitor the temperature of your furnace and protects it against overheating. They are designed to cut off the unit if it overheats.

M Oglesby :

Over heating can be caused by a clogged filter or blocked return register.

M Oglesby :

Lets first check the Manual reset rollout limit switches. They are small round metal disc looking devices that have two wires attached to them and a little button on top of them. They are usually located inside the furnace cabinet around the burner tray. They prevent the flame from exiting the burner area. Locate them and make sure the little buttons are pressed in. Remember there may be more than one.

M Oglesby :

Let me know when you find them.

Customer :

It run

Customer :

I have 2 paddle looking silver discs with two yellow wires out of them

M Oglesby :

Is the furnace working?

Customer :

no sorry that was a mistake

M Oglesby :

Do the little disc have buttons on them?

Customer :

no

Customer :

i dont see any discs with buttons

M Oglesby :

Ok lets find the main limit switch. It is a rectangular device that has two wires attached to it and sits inside the furnace cabinet on the back panel wall usually above the gas valve. Do you see It?

Customer :

Does it have the gas lines go threw it and some type of turn off switch on it

M Oglesby :

No that is the gas valve.

Customer :

i found it its attached by hex screws

M Oglesby :

I think it will be best for you to call a technician out to troubleshoot.

M Oglesby :

The issue that you have will require a technician to correct.

Customer :

ok

M Oglesby :

Please hit ACCEPT so I can be paid for my time. Thanks!

M Oglesby :

Make sure that you let the technician know that you have a open limit switch. That way he will know that you are not completely oblivious to what is going on.

M Oglesby :

He will be less likely to try and price gauge you.

M Oglesby, HVAC Technician
Category: HVAC
Satisfied Customers: 2038
Experience: Universally Certified HVACR Technician
M Oglesby and 3 other HVAC Specialists are ready to help you
Expert:  M Oglesby replied 3 years ago.
Since you have found the Liimit switch which some how I did not recieve that transmission until now, Remove the two wires that are attached to it and attach them together metal to metal. This is bypassing the limit switch. While the wires are attached, call for heat. Let me know if the heat comes on or not. If it does not, you will have to do all of the limit switches this way until you find out which one is the culprit. The Rollout limit switches as well.


Please remove negative feedback. That really hurts my reputation here. I really did not know that you found the limit switch and I apologize for you feeling as if you were robbed.

Edited by M Oglesby on 1/18/2011 at 3:58 PM EST

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