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M Oglesby
M Oglesby, HVAC Technician
Category: HVAC
Satisfied Customers: 2038
Experience:  Universally Certified HVACR Technician
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Thermal protection device open is what my diagnostic lights

Resolved Question:

Thermal protection device open is what my diagnostic lights are flashing in my American Standard gas furnace. furnace won't light
Submitted: 6 years ago.
Category: HVAC
Expert:  M Oglesby replied 6 years ago.

M Oglesby :

Hello I am here to assist you.

M Oglesby :

There are two kinds of limit switches. We will first locate the main limit switch and try to bypass it.

M Oglesby :

It is a rectangular device that has two wires attached to it and is usually located inside the furnace cabinet on the back panel wall just above the gas valve.

M Oglesby :

REmove the furnace panel door and locate it and let me know when you find it.

Customer:

found it

M Oglesby :

Remove the two wires that are attached to it and connect them together metal to metal very good.

M Oglesby :

While attached, call for heat. Cut the power first.

Customer:

ok

M Oglesby :

Let me know when you finish.

Customer:

ok done connecting the two together

M Oglesby :

Cut the power back on and turn the heat on and tell me what happens.

Customer:

it's working

M Oglesby :

That means you need a new Main Limit switch.

Customer:

can i leave this bypassed

M Oglesby :

You can get one here at www.AmericanHVACparts.com Have model number and serial number ready when ordering.

M Oglesby :

It is not recommended.

M Oglesby :

It is a safety device that protects the heater against over heating. It shuts the furnace off if it overheats.

M Oglesby :

If you do leave it bypassed, monitor it closely.

Customer:

ok thank you i will order it. Thank you

M Oglesby :

Please hit ACCEPT if you are satisfied with this answer. Bonuses and positive feedback are very much appreciated!

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