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Rick, HVAC Supervisor
Category: HVAC
Satisfied Customers: 20948
Experience:  40+ yrs. experience as a licensed oil & gas technician.
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I am getting 4 lights that indicating that my limit switch

Customer Question

I am getting 4 green lights that indicating that my limit switch is open, my furnace is not lighting.... What do i do?
Submitted: 1 year ago.
Category: HVAC
Expert:  BillyHvac replied 1 year ago.

hello, is the main blower running when 4 appears? and is filter clean?

Customer: replied 1 year ago.
filter is clean
Expert:  BillyHvac replied 1 year ago.

sorry I lost connection...did you see where I asked if blower is running? This is an overheat trip so before we go to switch I check blower

Customer: replied 1 year ago.
Blower is rolling. Pilot light is not firing though
Expert:  BillyHvac replied 1 year ago.

thank you, ***** ***** not see make or model...but on the front wall of furnace behind the gas you see a flat plate mounted flush on the wall with 2 wires?

Customer: replied 1 year ago.
Customer: replied 1 year ago.
You there???
Customer: replied 1 year ago.
It is 52 in my house right now and 31 outside.
Expert:  BillyHvac replied 1 year ago.

I apologize as I went offline at 11:30.

The picture that came through this morning is of an ac coil not the furnace.

Expert:  Rick replied 1 year ago.

It looks like my colleague has opted out. Do you still need help?

Customer: replied 1 year ago.
Expert:  Rick replied 1 year ago.

Ok, first I need the model number of your furnace not the AC coil. You can find the furnace model number inside the burner compartment on the rating tag.

Customer: replied 1 year ago.
I had to leave to the ski hill I can't really look at it. What does it mean when the limit switch is open? Will that prevent the unit from firing?
Expert:  Rick replied 1 year ago.

Yes an open limit switch will prevent the burners from firing. The limit switch opens if the furnace gets too hot. This can be caused by a dirty filter or maybe blocked heating vents or a clogged AC coil. This error could also be caused by a bad limit switch or a loose connection. On some models there is a flame roll out sensor that's also in the limit circuit which can trip and cause this error. The roll out switch is designed to trip if the burner flame "rolls out" of the burner chamber.

Customer: replied 1 year ago.
I cleaned the filters out. From the sounds of it I will need a technician to figure out the other things??
Expert:  Rick replied 1 year ago.

Probably best to call in a pro to check this out. The only thing that's easy to try is to see if the roll out switch(es) (see attached pictures)can be reset. They are located just above and outside the burner chamber. You push the small button between the 2 wires. If it clicks you have reset it. If it doesn't click then it wasn't tripped.